High-resolution ultra-thin led display for ar and vr devices and manufacturing method thereof

ABSTRACT

The present invention relates to a high-resolution ultra-thin light-emitting diode (LED) display and a manufacturing method thereof and relates to a display having very high resolving power and optical properties by introducing ultra-thin LED elements, and a manufacturing method capable of manufacturing the same with a very low defect rate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 2021-0141625, filed on Oct. 22, 2021, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND 1. Field of the Invention

The present invention relates to a display applied to augmented reality(AR) and virtual reality (VR) devices and relates to a high-resolutionultra-thin light-emitting element (LED) display which secures highresolving power by applying ultra-thin LEDs to LED elements of adisplay, and a manufacturing method thereof.

2. Discussion of Related Art

Augmented reality (AR) or virtual reality (VR) technology is technologyfor simultaneously showing the real world and a virtual image or showingthe virtual image, and is technology for showing a virtual objectoverlapping the real world. When a virtual image overlapping a realworld object in real time has a very high sense of realism, it can reachan extent where it is difficult for a wearer to distinguish thereal-world image from the virtually implemented image. Such technologyis also referred to as mixed reality (MR) technology. AR technology is ahybrid VR system that combines a real environment and a virtualenvironment, and research and development therefor is currently beingactively conducted in various countries.

AR or VR technology is implemented through a method of projectinginformation such as virtual images made of computer graphics. Virtualimages serve to enhance a visual effect of a specific element of a realenvironment or to display information related to the real world. Such ARtechnology is applied to a display mounted on a wearable device such asglasses or a helmet. AR and VR devices not only include all functions ofcurrent smartphones but also have a function of maximizing a visualinformation perception ability of a wearer. With the prospect that allcomputing interfaces will become AR and VR displays in the future, majorglobal companies are making developments with huge investments.

However, conventionally developed displays used in AR and VR devices andthose that are currently being developed have low resolving power, andthus a resolution thereof is not high.

When compared to existing liquid crystal displays (LCDs), liquidcrystal-on silicon (LCOS) devices, digital light processing (DLP)displays, and organic light-emitting displays (OLED) in terms ofbrightness, response speed, resolution, contrast, and the like for useas AR and VR displays, micro light-emitting diodes (LEDs) are known tobe the most efficient displays. However, in the case of micro LEDs, inorder to manufacture high-resolution displays and to satisfy theresolution of displays, it is known that micro-LEDs with a size of 1 μmto 5 μm are required, but in manufacturing a subpixel using micro-LEDs,there is a problem in that display defects occur due to display darkspots caused by process defects (vacancies of LED elements in the pixel,misalignment error, and the like) during micro-LED transfer (see FIG.1A).

There are a wide variety of types of LEDs that have been developed sofar. In particular, among various LEDs, micro-LEDs and nano-LEDs areable to implement excellent color and high efficiency and areeco-friendly materials and thus are used as core materials for variouslight sources and displays. According to such market conditions,recently, research on developing a new nanorod LED structure or ananocable LED with a shell coated through a new manufacturing processhas been underway.

In line with such research in the field of materials, displaytelevisions (TVs) using red, green, and blue micro-LEDs have recentlybeen commercialized. Displays and various light sources using micro-LEDshave advantages such as high performance characteristics, a very longtheoretical lifetime, and very high theoretical efficiency. However,since micro-LEDs should be individually disposed on a miniaturizedelectrode having a limited area, due to a limitation in processtechnology in consideration of high unit costs, a high process defectrate, and low productivity, an electrode assembly implemented byarranging micro-LEDs on an electrode with pick and place technology isdifficult to manufacture into true high-resolution commercial displaysfrom smartphones to TVs or light sources having various sizes, shapes,and brightness. In addition, it is more difficult to individuallyarrange nano-LEDs, which are implemented to be smaller than micro-LEDs,on an electrode with pick and place technology as in micro-LEDs.

In order to overcome such difficulties, Korean Patent Publication No.10-1490758 by the present inventor discloses an ultra-small LEDelectrode assembly manufactured through a method of dropping a solutionin which nanorod-type LEDs are mixed on electrodes and then forming anelectric field between two different electrodes to self-alignnanorod-type LED elements on the electrodes. However, in such disclosedtechnology, since the LED elements are aligned through an electricfield, the LED elements should have a rod shape with a large aspectratio, which is formed to be elongated in one direction. Since such arod-type LED element having a large aspect ratio is easily precipitatedin a solvent, it is difficult to make the LED element into an ink, andthus it is not easy to implement a large-area electrode assembly throughinkjet printing.

In addition, since elements lie down to be assembled on two differentelectrodes, that is, since the elements are assembled with a stackingdirection of each semiconductor layer in the element parallel to a mainsurface of the electrode, an area from which light is extracted issmall, resulting in a problem of lower efficiency. Specifically, amethod of manufacturing a nanorod-type LED element using an LED waferthrough a top-down method in which a nano-patterning process and dryetching/wet etching are mixed, or growing a nanorod-type LED elementdirectly on a substrate (base substrate) through a bottom-up method isknown. In such nanorod-type LEDs, since a major axis of the LED matchesa stacking direction, that is, in a stacking direction of each layer ina p-GaN/InGaN multi-quantum well (MQW)/n-GaN, and a p-GaN/InGaNmulti-quantum well (MQW)/n-GaN/InGaN stack structure, a light emittingarea is narrow, surface defects have a relatively large influence on adecrease in efficiency. Since it is difficult to optimize arecombination rate of electrons and holes, there is a problem in thatluminous efficiency is considerably lower than the original efficiencyof a wafer.

Furthermore, since two different electrodes formed to allow ananorod-type LED element to emit light should be formed to be coplanar,there is a problem in that electrode design is not easy.

RELATED ART DOCUMENTS Patent Documents

Korean Patent Publication No. 10-1490758 (published on Mar. 26, 2019)2019)

SUMMARY OF THE INVENTION

The inventor of the present invention has developed a new ultra-thin LEDelectrode assembly in which problems of display defects, which arecaused by low resolving power of a display manufactured using microlight-emitting diodes (LEDs), vacancies of LED elements in a pixel,misalignment, and the like, are solved. The present invention isdirected to providing a display for augmented reality (AR) and virtualreality (VR) devices to which such an ultra-thin LED electrode assemblyis applied, and a manufacturing method thereof.

According to an aspect of the present invention, there is provided ahigh-resolution ultra-thin LED display for AR and virtual reality VRdevices, including an ultra-thin LED electrode assembly which includes aplurality of lower electrodes formed on a substrate, a plurality ofpixel units formed on the lower electrodes, an insulating layer formedon the substrate and the plurality of pixel units, and a plurality ofupper electrodes formed on the insulating layer, wherein each of theplurality of pixel units includes subpixel units each including aplurality of ultra-thin LED elements.

The subpixel unit may include three or more ultra-thin LED elements, andthe ultra-thin LED element may include at least one selected from amongan ultra-thin blue LED element, an ultra-thin green LED element, and anultra-thin red LED element.

Each of the plurality of pixel units may include three or four subpixelunits, and each of the three or four subpixel units may include 3 to 30ultra-thin LED elements.

Each of the three or four subpixel units may have a circular shape, arectangular shape, or a square shape.

Each of the three or four subpixel units may have an aspect ratio of1:1.0 to 1:10.0.

Each of the plurality of pixel units may include three subpixel units,and the three subpixel units may include a first subpixel unit includingan ultra-thin blue LED element, a second subpixel unit including anultra-thin green LED element, and a third subpixel unit including anultra-thin red LED element.

All of the three or four subpixel units may include the ultra-thin blueLED element.

When all of the three or four subpixel units include the ultra-thin blueLED element, at least one color conversion layer selected from a greencolor conversion layer and a red color conversion layer may be furtherstacked on the upper electrode.

At least one pass filter selected from a short wavelength pass filter(SWPF) and a long wavelength pass filter (LWPF) may be further formedbetween the upper electrode and the color conversion layer.

Each of the plurality of ultra-thin LED elements constituting thesubpixel unit of the high-resolution ultra-thin LED display of thepresent invention may include a first conductive semiconductor layer, aphotoactive layer, and a second conductive semiconductor layer which arestacked.

The ultra-thin LED elements may be erected and disposed in the subpixelunit such that the first conductive semiconductor layer of theultra-thin LED element faces the lower electrode.

A cross-sectional shape of the ultra-thin LED element may include atleast one shape selected from among a circular shape, an oval shape, anda polygonal shape (a triangular shape, a square shape, a pentagonalshape, a hexagonal shape, an octagonal shape, a decagonal shape, atrapezoidal shape, a rhombic shape, or a star shape), and the pluralityof ultra-thin LED elements may be provided as elements having the samecross-sectional shape or may be provided by mixing elements havingdifferent cross-sectional shapes.

The ultra-thin LED element may include at least one selected from a dotor disc LED element which has a thickness of 2.000 nm or less in astacking direction of layers, wherein the dot LED element has a ratiobetween the thickness and a length of a major axis in a cross sectionperpendicular to the stacking direction in a range of 1:0.5 to 1:1.5,and the disc LED element has a ratio between the thickness and a lengthof a major axis in a cross section perpendicular to the stackingdirection in a range of 1:1.5 to 1:5.0, and a micro-nanofin LED elementwhich has a thickness of 100 nm to 2,000 nm in a stacking direction oflayers and in which a length of a major axis cross section perpendicularto the stacking direction is in a range of 100 nm to 6,000 nm, and aratio between the thickness and the length of the major axis is 1:3 ormore.

The LED electrode assembly may include a lower electrode line includingone or more lower electrodes, the plurality of ultra-thin LED elementserected and arranged on the lower electrodes in a stacking direction oflayers, and an upper electrode line including one or more upperelectrodes disposed on the plurality of ultra-thin LED elements.

The ultra-thin LED element may further include an arrangement guidelayer, which is for erecting and arranging the ultra-thin LED element ina thickness direction thereof, at one side of the ultra-thin LED elementin the thickness direction and one side or both sides of a region in thelower electrode in which the ultra-thin LED element is to be disposed.

The arrangement guide layer may be a magnetic layer, a charge layer, ora bonding layer.

The ultra-thin LED element may have a maximum surface area of ⅓ or lessof a subpixel area.

The first conductive semiconductor layer of the ultra-thin LED elementmay be an n-type III-nitride semiconductor layer, and the ultra-thin LEDelement may further include an electron delay layer on an oppositesurface opposite to one surface of the first conductive semiconductorlayer adjacent to the photoactive layer such that the numbers ofelectrons and holes recombined in the photoactive layer are balanced.

The electron delay layer may be a III-nitride semiconductor having alower doping concentration than the first conductive semiconductorlayer.

The second conductive semiconductor layer of the ultra-thin LED elementmay be a p-type III-nitride semiconductor layer, and the ultra-thin LEDelement may further include an electron delay layer on an oppositesurface opposite to one surface of the second conductive semiconductorlayer adjacent to the photoactive layer such that the numbers ofelectrons and holes recombined in the photoactive layer are balanced.

The electron delay layer may include at least one selected from amongCdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, GaTe, SiC, ZnO, ZnMgO, SnO₂,TiO₂, In₂O₃, Ga₂O₃, silicon (Si), poly(para-phenylene vinylene) and aderivative thereof, a poly(3-alkylthiophene), and poly(paraphenylene).

The first conductive semiconductor layer of the ultra-thin LED elementmay be an n-type III-nitride semiconductor layer, the second conductivesemiconductor layer may be a p-type III-nitride semiconductor layer, andthe ultra-thin LED element may further include at least one film of ahole pushing film which surrounds an exposed side surface of the secondconductive semiconductor layer or the exposed side surface of the secondconductive semiconductor layer and an exposed side surface of at least aportion of the photoactive layer to move holes at a side of the exposedside surface toward a center and an electron pushing film whichsurrounds an exposed side surface of the first conductive semiconductorlayer to move electrons at a side of the exposed side surface sidetoward a center.

The ultra-thin LED element may include both the hole pushing film andthe electron pushing film, and the electron pushing film may be providedas an outermost film surrounding the side surfaces of the firstconductive semiconductor layer, the photoactive layer, and the secondconductive semiconductor layer.

The hole pushing film may include at least one selected from amongAlN_(x), ZrO₂, MoO, Sc₂O₃, La₂O₃, MgO, Y₂O₃, Al₂O₃, Ga₂O₃, TiO₂, ZnS,Ta₂O₅, and n-MoS₂.

The electron pushing film may include at least one selected from amongAl₂O₃, HfO₂, SiN_(x), SiO₂, ZrO₂, Sc₂O₃, AlN_(x), and Ga₂O₃.

When the ultra-thin LED element is a micro-nanofin LED element, themicro-nanofin LED element may include a polarization inducing layer thatis further stacked on the second conductive semiconductor layer.

When the ultra-thin LED element is the micro-nanofin LED element, thefirst conductive semiconductor layer or the polarization inducing layerof the micro-nanofin LED element may be disposed in contact with atleast two adjacent lower electrodes.

The polarization inducing layer may be provided such that electricalpolarities of both end portions of the micro-nanofin LED element in alength direction are different.

The polarization inducing layer may include a first polarizationinducing layer and a second polarization inducing layer which aredisposed adjacent to each other in the length direction of themicro-nanofin LED element, and the first polarization-inducing layer andthe second polarization-inducing layer may have different electricalpolarities. In this case, as an example, the first polarization inducinglayer may be made of indium tin oxide (ITO), and the second polarizationinducing layer may be made of a metal, a dielectric, or a semiconductor.

The micro-nanofin LED element may have a length of 100 nm to 6,000 nmand a thickness of 100 nm to 2,000 nm.

A ratio of the length and the thickness of the micro-nanofin LED elementmay be 3:1 or more.

A protrusion having a certain width and thickness may be formed on alower surface of the first conductive semiconductor layer of themicro-nanofin LED element in an element direction.

A width of the protrusion may have a length of 50% or less of a width ofthe micro-nanofin LED element.

A light emitting area of the micro-nanofin LED element may exceed twicean area of a longitudinal cross section of the micro-nanofin LEDelement.

Pores may be formed in a portion of the first conductive semiconductorlayer (n-type conductive semiconductor layer) of the ultra-thin LEDelement (dot, disc, and/or micro-nanofin type LED element).

The LED electrode assembly may be formed on a flexible substrate.

The high-resolution ultra-thin LED display may have a resolving power of450 pixels per inch (PPI) to 3,000 PPI.

The above-described high-resolution ultra-thin LED display of thepresent invention may be used in display panels for AR and VR devices.

According to another aspect of the present invention, there is provideda manufacturing method of a high-resolution ultra-thin LED display,which includes an ultra-thin LED electrode assembly, for AR and VRdevices, wherein an ultra-thin LED electrode assembly may be formed byperforming a process which includes operation 1 of providing a lowerelectrode line including a lower electrode, operation 2 of forming aplurality of pixel units on the lower electrode, and operation 3 offorming an upper electrode line, which includes upper electrodes, to beelectrically connected to an opposite side of an ultra-thin LED elementopposite to one side of an ultra-thin LED element assembled on the lowerelectrodes.

The process may further include an operation of filling a periphery ofthe ultra-thin LED element in each of the plurality of pixel units withan insulator to form an insulating layer between operations 2 and 3.

Each of the plurality of pixel units in operation 2 may be formed ofsubpixel units each including a plurality of ultra-thin LED elements,and the subpixel units may be formed by printing the plurality ofultra-thin LED elements on the lower electrodes through an inkjetprinting method, a laser-assisted transfer printing method, a stamptransfer printing method, a magnetic field induction printing method,and/or an electric field induction printing method.

When a printing method is the laser-assisted multi-chip transferprinting method, a process including operation 1 of providing aplurality of lower electrodes formed on a substrate and operation 2 ofperforming transferring through the laser-assisted multi-chip transferprinting method to form a plurality of pixel units on the lowerelectrodes may be performed.

In the laser-assisted multi-chip transfer printing method, in operation2, each of the plurality of pixel units may include a plurality ofultra-thin LED elements.

In the laser-assisted multi-chip transfer printing method, in operation2, a laser may be radiated onto one surface of a transfer film throughopenings of a mask to transfer the ultra-thin LED elements onto thelower electrode and to form the pixel unit including the plurality ofultra-thin LED elements on the lower electrode. The transfer film mayinclude a donor film and the plurality of ultra-thin LED elementsarranged on the donor film, and the transferring may be performed byradiating a laser from below the donor film.

In the laser-assisted multi-chip transfer printing method, each of theplurality of ultra-thin LED elements may include a second conductivesemiconductor layer, a photoactive layer, and a first conductivesemiconductor layer which are stacked. The ultra-thin LED element may bedisposed such that the second conductive semiconductor layer or thefirst conductive semiconductor layer of the ultra-thin LED element facesthe donor film.

In the laser-assisted multi-chip transfer printing method, the donorfilm may include a polydimethylsiloxane stamp (PDMS) film, a polyimidefilm including a dynamic release layer, an elastomeric microstructurestamp film, or a shape memory polymer film.

In the laser-assisted multi-chip transfer printing method, in operation2, the plurality of openings may be formed in the mask, and a laser maybe radiated through each of the plurality of openings to simultaneouslytransfer three or more ultra-thin LED elements per opening on the lowerelectrode.

When the printing method is the laser-assisted multi-chip transferprinting method and the ultra-thin LED element is a dot or disc LEDelement, in operation 2, operation 2-1 of processing an ink compositionincluding the plurality of ultra-thin LED elements on the lowerelectrodes, and operation 2-2 of erecting the ultra-thin LED elements ina thickness direction thereof and assembling the ultra-thin LED elementson the lower electrodes may be performed.

In operation 2-1, a magnetic layer may further be provided at one sideof the ultra-thin LED element in the thickness direction and in anarrangement area on the lower electrode in which the ultra-thin LEDelement is to be disposed. In operation 2-2, an electric field may beformed in a direction perpendicular to a main surface of the lowerelectrode to erect and assemble the ultra-thin LED element on the lowerelectrode in the thickness direction so that the ultra-thin LED elementis moved to the arrangement region and erected and disposed in thethickness direction.

In operation 2-1, a first charge layer having positive or negativecharges may further be provided at one side of the ultra-thin LEDelement in the thickness direction, and a second charge layer that hascharges opposite to those of the first charge layer may be provided inan arrangement region on the lower electrode. In operation 2-2, anelectric field may be formed in a direction perpendicular to a mainsurface of the lower electrode so that the ultra-thin LED element ismoved to the arrangement region and erected and disposed in thethickness direction.

In operation 2-2, by using a chemical bond through a bonding layerbetween one side of the ultra-thin LED element in the thicknessdirection and the arrangement region on the lower electrode in which theultra-thin LED element is to be disposed, the ultra-thin LED element maybe erected and assembled in the arrangement region. The bonding layermay be provided at one side of the ultra-thin LED element in thethickness direction thereof and one side or both sides of thearrangement region.

When the printing method is a laser-assisted multi-chip transferprinting method and the ultra-thin LED element is a micro-nanofin LEDelement, the LED electrode assembly may be manufactured by performing aprocess which includes operation 1 of injecting an ink compositionincluding a plurality of micro-nanofin LED elements onto a lowerelectrode line including a plurality of lower electrodes spaced acertain interval from each other in a horizontal direction, operation 2of applying an assembly voltage to the lower electrode line andself-aligning the micro-nanofin LED elements such that a firstconductive semiconductor layer or a polarization inducing layer of themicro-nanofin LED element in a solution comes into contact with at leasttwo adjacent lower electrodes, and operation 3 of forming an upperelectrode line on the plurality of self-aligned micro-nanofin LEDelements.

In operation 2, operation 2-1 of applying an assembly voltage to thelower electrode line and self-aligning the micro-nanofin LED elementssuch that the first conductive semiconductor laver or the polarizationinducing layer of the micro-nanofin LED element in the solution comesinto contact with at least two adjacent lower electrodes, operation 2-2of forming a conducting metal layer for connecting a side surface of thelower electrode line or the polarization inducing layer of eachmicro-nanofin LED element, which will be in contact with at least twolower electrodes, to the at least two lower electrodes, and operation2-3 of forming an insulating layer on the lower electrode line to notcover an upper surface of the plurality of self-aligned micro-nanofinLED element may be performed.

Next, terms used in the present invention will be defined.

In descriptions of exemplary embodiments according to the presentinvention, it will be understood that, when a layer, a region, apattern, or a substrate is referred to as being “on,” “above,” “under,”or “below” another layer, region, or pattern, the terminology of “on,”“above,” “under,” or “below” includes both the meanings of “directly”and “indirectly.”

Meanwhile, the present invention was researched under support of thefollowing Korea R&D Project.

1. [Korea R&D Project Supporting the Present Invention]

[Project Series Number] 1711130702

[Project Number] 2021R1A2C2009521

[Government Department Name] The Ministry of Science and ICT

[Project Management Administration Authority Name] National ResearchFoundation of Korea

[Research Program Name] Middle Career Researcher Support Project

[Research Project Name] Development of Dot-LED Material and DisplaySource/Application Technology

[Contribution Ratio] 1/2

[Name of Project Execution Organization] Kookmin University IndustryAcademy Cooperation Foundation

[Period of Research] Mar. 1, 2021 to Feb. 28, 2022

2. [Korea R&D Project Supporting the Present Invention]

[Project Series Number] 1711105790

[Project Number] 2016R1A5A1012966

[Government Department Name] The Ministry of Science and ICT

[Project Management Administration Authority Name] National ResearchFoundation of Korea

[Research Program Name] Science and Engineering Field (S/ERC)

[Research Project Name] Hybrid Device-based Circadian-ICT ResearchCenter

[Contribution Ratio] 1/2

[[Name of Project Execution Organization] Kookmin University IndustryAcademy Cooperation Foundation

[Period of Research] Jan. 1, 2021 to Dec. 31, 2021

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are schematic views each illustrating an example ofprocess defects when light-emitting diode (LED) elements formanufacturing a display are transferred, wherein FIG. 1A illustrates anexample of defects that occur when an existing micro-LED element isused, and FIG. 1B is an example of defects that occur when an ultra-thinLED element of the present invention is used as an LED element.

FIG. 2A and FIG. 2B show views of an ultra-thin LED electrode assemblyusing ultra-thin LED elements (first type, dot type, or disc type)according to an exemplary embodiment of the present invention, whereinFIG. 2A is a plan view of the ultra-thin LED electrode assembly, andFIG. 2B is a cross-sectional view along boundary line X-X′ of FIG. 2A.

FIG. 3 is a perspective view of an ultra-thin LED element (first type)used in an exemplary embodiment of the present invention.

FIG. 4 is a cross-sectional view along boundary line Y-Y′ of FIG. 3 .

FIG. 5A, FIG. 5B, and FIG. 5C are views of various examples of anarrangement guide layer to be provided in the ultra-thin LED element(first type) used in an exemplary embodiment of the present invention.

FIG. 6 is a schematic view for describing a balance between electronsand holes in an LED element.

FIG. 7 is a perspective view of an ultra-thin LED element (first type)used in an exemplary embodiment of the present invention.

FIG. 8 is a cross-sectional view of an ultra-thin LED element (firsttype) used in an exemplary embodiment of the present invention.

FIG. 9 and FIG. 10 show schematic views of a manufacturing method 1 ofan ultra-thin LED element (first type) used in an exemplary embodimentof the present invention.

FIG. 11 shows schematic views of a manufacturing method 2 of anultra-thin LED element (first type) used in an exemplary embodiment ofthe present invention.

FIG. 12 shows schematic views of a manufacturing method of an ultra-thinLED element (first type) used in an exemplary embodiment of the presentinvention.

FIG. 13 , FIG. 14 , and FIG. 15 show schematic views illustratingvarious examples of an operation of a manufacturing method of anultra-thin LED electrode assembly using ultra-thin LED elements (secondtype or micro-nanofin type) according to an exemplary embodiment of thepresent invention.

FIG. 16A and FIG. 16B show views of a micro-nanofin LED electrodeassembly according to an exemplary embodiment of the present invention,wherein FIG. 16A is a plan view of the micro-nanofin LED electrodeassembly, and FIG. 16B is a cross-sectional view along boundary lineX-X′ of FIG. 16A.

FIG. 17 , FIG. 18 , and FIG. 19 are a perspective view of amicro-nanofin LED element included in an exemplary embodiment of thepresent invention, a cross-sectional view along boundary line X-X′ ofFIG. 18 , and a cross-sectional view along boundary line Y-Y′ of FIG. 19.

FIG. 20A and FIG. 20B show a schematic view of a first rod-type elementin which a first conductive semiconductor layer, a photoactive layer,and a second conductive semiconductor layer are stacked in a thicknessdirection thereof and a schematic view of a second rod-type element inwhich a first conductive semiconductor laver, a photoactive layer, and asecond conductive semiconductor layer are stacked in a length directionthereof.

FIG. 21 shows schematic views of a manufacturing process of amicro-nanofin LED element included in an exemplary embodiment of thepresent invention.

FIG. 22A, FIG. 22B, and FIG. 22C and FIG. 23A, FIG. 23B, and FIG. 23Cshow scanning electron microscope (SEM) images at a specific operationof a manufacturing method of an ultra-thin LED element (first type) usedin an exemplary embodiment of the present invention. Here, FIG. 22B is amagnified view of FIG. 22A, FIG. 23B is a magnified view of FIG. 23A,and FIG. 22C is a top-down view of FIG. 22A, and FIG. 23C is a top-downview of FIG. 23A.

FIG. 24A and FIG. 24B show SEM images of an ultra-thin LED element(first type) used in an exemplary embodiment of the present invention.

FIG. 25A and FIG. 25B show SEM images of an LED wafer remaining after anultra-thin LED element is manufactured in a manufacturing process of theultra-thin LED element (first type) used in an exemplary embodiment ofthe present invention.

FIG. 26 is an absorbance graph for each time in which a spectral area ofa visible light region of 380 nm and 780 nm is normalized usingabsorbance for each wavelength measured for each time in an inkcomposition in which an ultra-thin LED element (first type) and arod-type LED element are each dispersed in acetone.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail so as to be easily practiced by a person of ordinaryskill in the art to which the present invention pertains. It should beunderstood that the present invention may be embodied in variousdifferent forms and is not limited to the following exemplaryembodiments.

As shown in a schematic view of FIG. 1A, in a display manufactured usingexisting micro-light-emitting diodes (LEDs), when an electrode LEDassembly is formed, since each pixel includes one micro-LED element or asmall number of micro-LED elements, there has been a problem in thatdark spots occur due to omission (vacancies) of LED elements duringtransfer, deviation thereof from an electrode line (misalignment), andthe like. However, as shown in a schematic view of FIG. 1B, in thepresent invention, since an electrode LED assembly is manufactured usingultra-thin LED elements, one pixel unit includes a plurality ofsubpixels, and one subpixel includes a plurality of ultra-thin LEDelements. Thus, even when some of the LED elements are omitted duringtransfer or deviate from an electrode line, since the LED elements areoperated without vacancies or misalignment in a pixel unit, dark spotsare not generated, thereby preventing display defects. Furthermore, thepresent invention may provide a high-resolution LED display capable ofsecuring high resolving power (pixels per inch (PPI)).

The high-resolution ultra-thin LED display of the present inventionincludes an ultra-thin LED electrode assembly including ultra-thin LEDelements.

As shown in a schematic view of FIG. 2A, the ultra-thin LED electrodeassembly includes an ultra-thin LED electrode assembly including aplurality of lower electrodes 310 formed (provided) on a substrate 400,a plurality of pixel units formed on the lower electrodes, an insulatinglayer 600 formed on the substrate and the plurality of pixel units, anda plurality of upper electrodes 320 formed on the insulating layer. Eachof the plurality of pixel units includes subpixel units each including aplurality of ultra-thin LED elements 100.

The subpixel unit may include three or more ultra-thin LED elements,preferably 3 to 30 ultra-thin LED elements, and more preferably 10 to 30ultra-thin LED elements, and the ultra-thin LED element may include atleast one LED element selected from among an ultra-thin blue LEDelement, an ultra-thin green LED element, and an ultra-thin red LEDelement.

In addition, each of the plurality of pixel units may include three orfour subpixel units, and each of the three or four subpixel units mayinclude three or more ultra-thin LED elements, preferably 3 to 30ultra-thin LED elements, and more preferably 10 to 30 ultra-thin LEDelements.

According to an exemplary embodiment, for example, as shown in aschematic view of FIG. 2B, when the pixel unit includes three subpixelunits, the pixel unit may include a first subpixel unit, a secondsubpixel unit, and a third subpixel unit.

Each of the two or three subpixel units may have a rectangular shape ora square shape, and when each of the three or four subpixel units hasthe rectangular shape, each of the three or four subpixel units may havean aspect ratio of 1:1.0 to 1:10.0.

In addition, each of the plurality of pixel units may include the firstsubpixel unit including the ultra-thin blue LED element, the secondsubpixel unit including the ultra-thin green LED element, and the thirdsubpixel unit including the ultra-thin red LED element.

In addition, when the display is a color-by-blue type display, the twoor three subpixel units constituting each of the plurality of pixelunits may all include the ultra-thin blue LED element, and in this case,one or more color conversion layers selected from a green colorconversion layer and a red color conversion layer may be further stackedon the upper electrode.

Any material that may be used in a color-by-blue manner may be used forthe green color conversion layer without limitation. As an exemplaryexample, the green color conversion layer may include at least onephosphor selected from among SrGa₂S₄:Eu, (Sr,Ca)₃SiO₅:Eu,(Sr,Ba,Ca)SiO₄:Eu, Li₂SrSiO₄:Eu, Sr₃SiO₄:Ce,Li, β-SiALON:Eu, CaSc₂O₄:Ce,Ca₃Sc₂Si₃O₁₂:Ce, Caα-SiALON:Yb, Caα-SiALON:Eu, Liα-SiALON:Eu,TaAl₅O₁₂:Ce, Sr₂Si₅N₈:Ce, SrSi₂O₂N₂:Eu, BaSi₂O₂N₂:Eu, Ba₃Si₆O₁₂N₂:Eu,γ-AlON:Mn, and γ-AlON:Mn,Mg, but the present invention is not limitedthereto.

Any material that may be used in a color-by-blue manner may be used forthe green color conversion layer without limitation. As anotherexemplary example, the green color conversion layer may include one ormore quantum dots or nanoparticles selected from among InP/ZnSe/ZnSquantum dots, InP/GaP/ZnS quantum dots, ZnSe/ZnS quantum dots, CsPbBr₃nanoparticles, and Cs₃MnBr₅ nanoparticles, but the present invention isnot limited thereto.

Any material that may be used in a color-by-blue manner may be used forthe red color conversion layer without limitation. As an exemplaryexample, the red color conversion layer may include at least onephosphor selected from among (Sr,Ca)AlSiN₃:Eu, CaAlSiN₃:Eu, (Sr,Ca)S:Eu,CaSiN₂:Ce, SrSiN₂:Eu, Ba₂Si₅N₈:Eu, CaS:Eu, CaS:Eu,Ce, SrS:Eu, SrS:Eu,Ce,and Sr₂Si₅N₈:Eu, but the present invention is not limited thereto. Foranother example, the red conversion layer may include one or morequantum dots or nanoparticles selected from among InP/ZnSe/ZnS quantumdots, InP/GaP/ZnS quantum dots, ZnSe/ZnS quantum dots, CsPb(Br,I)₃nanoparticles, and CsMnBr₃ nanoparticles, but the present invention isnot limited thereto.

In addition, at least one pass filter selected from a short wavelengthpass filter (SWPF) and a long wavelength pass filter (LWPF) may befurther formed between the upper electrode and the color conversionlayer. The short wavelength pass filter may be a multi-layered film inwhich thin films made of a high refractive material and a low refractivematerial are repeated. As an exemplary example, the short wavelengthpass filter may be [0.5SiO₂/TiO₂/0.5SiO₂]^(m) (m=the number of repeatedlayers and m is 7 or more) but is not limited thereto. In addition, thelong wavelength pass filter may be a multi-layered film in which thinfilms made of a high refractive material and a low refractive materialare repeated. As a preferred example, the long wavelength pass filtermay be [0.5TiO₂/SiO₂/0.5TiO₂]^(m) (m=the number of repeated layers and mis 7 or more).

Each of the plurality of ultra-thin LED elements constituting thesubpixel unit is an LED element in which a first conductivesemiconductor layer, a photoactive layer, and a second conductivesemiconductor layer are stacked. The ultra-thin LED element may beerected and disposed in the subpixel unit such that the first conductivesemiconductor layer of the ultra-thin LED element faces the lowerelectrode.

A cross-sectional shape of the ultra-thin LED element may include atleast one shape selected from among a circular shape, an oval shape, anda polygonal shape (a triangular shape, a square shape, a pentagonalshape, a hexagonal shape, an octagonal shape, a decagonal shape, atrapezoidal shape, a rhombic shape, or a star shape), and the pluralityof ultra-thin LED elements may be provided as elements having the samecross-sectional shape, or elements having different cross-sectionalshapes may be mixed to constitute the subpixel unit.

In addition, the ultra-thin LED element may be a dot type or disc typeLED element (first type), or a micro-nanofin LED element (second type).

In the present invention, the ultra-thin LED element may further includean arrangement guide layer, which is for erecting and arranging theultra-thin LED element in a thickness direction thereof, at one side ofthe ultra-thin LED element in the thickness direction and one side orboth sides of a region on the lower electrode in which the ultra-thinLED element is to be disposed.

The arrangement guide layer may be a magnetic layer, a charge layer, ora bonding layer.

In addition, a maximum surface area of the ultra-thin LED element may be⅓ or less of an area of the subpixel, preferably in a range of 1/50 to ⅓thereof, and more preferably in a range of 1/30 to ⅓ thereof.

The first conductive semiconductor layer of the ultra-thin LED elementis an n-type III-nitride semiconductor layer. The ultra-thin LED elementmay further include an electron delay layer on an opposite surfaceopposite to one surface of the first conductive semiconductor layeradjacent to the photoactive layer such that the numbers of electrons andholes recombined in the photoactive layer are balanced.

In addition, the electron delay layer may be a III-nitride semiconductorhaving a lower doping concentration than the first conductivesemiconductor layer.

Furthermore, the second conductive semiconductor layer of the ultra-thinLED element is a p-type III-nitride semiconductor layer. The ultra-thinLED element may further include an electron delay layer on an oppositesurface opposite to one surface of the second conductive semiconductorlayer adjacent to the photoactive layer such that the numbers ofelectrons and holes recombined in the photoactive layer are balanced.

In addition, the electron delay layer may include at least one selectedfrom among CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, GaTe, SIC, ZnO, ZnMgO,SnO₂, TiO₂, In₂O₃, Ga₂O₃, silicon (Si), poly(para-phenylene vinylene) ora derivative thereof, a poly(3-alkylthiophene), and poly(paraphenylene).

Furthermore, the first conductive semiconductor layer of the ultra-thinLED element is an n-type III-nitride semiconductor layer, and the secondconductive semiconductor layer thereof is a p-type III-nitridesemiconductor layer. The ultra-thin LED element may further include atleast one thin film of a hole pushing film which surrounds an exposedside surface of the second conductive semiconductor layer or the exposedside surface of the second conductive semiconductor layer and an exposedside surface of at least a portion of the photoactive layer to moveholes at a side of the exposed side surface toward the center and anelectron pushing film which surrounds an exposed side surface of thefirst conductive semiconductor layer to move electrons at a side of theexposed side surface toward the center.

In addition, the ultra-thin LED element may include both the holepushing film and the electron pushing film, and the electron pushingfilm may be provided as an outermost film surrounding the side surfacesof the first conductive semiconductor layer, the photoactive layer, andthe second conductive semiconductor layer.

Furthermore, the hole pushing film may include at least one selectedfrom among AlN_(x), ZrO₂, MoO, Sc₂O₃, La₂O₃, MgO, Y₂O₃, Al₂O₃, Ga₂O₃,TiO₂, ZnS, Ta₂O₅, and n-MoS₂.

Also, the electron pushing film may include at least one selected fromamong Al₂O₃, HfO₂, SiN_(x), SiO₂, ZrO₂, Sc₂O₃, AlN_(x), and Ga₂O₃.

In the ultra-thin LED electrode assembly, the substrate is preferably aflexible substrate.

In addition, the LED electrode assembly may be encapsulated with anencapsulant.

In the above-described high-resolution ultra-thin LED display includingthe ultra-thin LED electrode assembly, the ultra-thin LED electrodeassembly may be manufactured through a process including operation 1 ofproviding a lower electrode line including lower electrodes, operation 2of forming a plurality of pixel units on the lower electrodes, andoperation 3 of forming an upper electrode line, which includes upperelectrodes, to be electrically connected to an opposite side of anultra-thin LED element opposite to one side of the ultra-thin LEDelement assembled on the lower electrode.

The process may further include an operation of filling a periphery ofthe ultra-thin LED element in each of the plurality of pixel units withan insulator to form an insulating layer between operations 2 and 3.

Each of the plurality of pixel units in operation 2 may be formed ofsubpixel units each including a plurality of ultra-thin LED elements.The subpixel unit may be formed by printing the plurality of ultra-thinLED elements on the lower electrodes through an inkjet printing method,a laser-assisted multi-chip transfer printing method, a stamp transferprinting method, a magnetic field induction printing method, and/or anelectric field induction printing method.

An exemplary embodiment of the laser-assisted multi-chip transferprinting method among the printing methods will be described as follows.

The ultra-thin LED electrode assembly of the present invention may bemanufactured by performing a process including operation 1 of providinga plurality of lower electrodes formed on a substrate and operation 2 ofperforming transferring through the laser-assisted multi-chip transferprinting method to form a plurality of pixel units on the lowerelectrodes.

In addition, after operation 2 is performed, a process includingoperation 3 of filling a periphery of an ultra-thin LED element with aninsulator to form an insulating layer and operation 4 of forming anupper electrode to be electrically connected to an opposite side of theultra-thin LED element opposite to one side of the ultra-thin LEDelement assembled on the lower electrode.

Each of the plurality of pixel units in operation 2 may be formed ofsubpixel units each including a plurality of ultra-thin LED elements.The subpixel units may be formed by printing the plurality of ultra-thinLED elements on the lower electrodes through the laser-assistedmulti-chip transfer printing method.

More specifically, in the laser-assisted multi-chip transfer printingmethod, a laser may be radiated onto one surface of a transfer filmthrough openings of a mask having a plurality of openings to transferthe ultra-thin LED elements onto the lower electrode and to form thepixel unit including the plurality of ultra-thin LED elements on thelower electrodes. The transfer film may include a donor film and theplurality of ultra-thin LED elements arranged on the donor film, and thetransferring may be performed by radiating a laser from below the donorfilm.

A laser may be radiated through each of the plurality of openings tosimultaneously transfer three or more ultra-thin LED elements peropening on the lower electrodes, and in this case, an amount of thetransferred ultra-thin LED elements may be controlled by adjusting thesize of the opening of the mask and the arrangement, number, and/or sizeof the ultra-thin LED elements formed on the donor film of the transferfilm.

In this case, the transfer film may include the donor film and theplurality of ultra-thin LED elements arranged on the donor film, and thetransferring may be performed by radiating a laser from below the donorfilm.

In addition, in each of the plurality of ultra-thin LED elements, asecond conductive semiconductor layer, a photoactive layer, and a firstconductive semiconductor layer are stacked. When the ultra-thin LEDelement is transferred by radiating a laser toward the donor film of thetransfer film, the order of the layers in the ultra-thin LED element isreversed. Thus, it is possible to form and arrange the ultra-thin LEDelement having a form in which the first conductive semiconductor layer,the photoactive layer, and the second conductive semiconductor layer aresequentially stacked on the lower electrode.

In this case, the laser-assisted multi-chip transfer printing method maybe performed in various ways. As described above, it is preferable thatthe donor film in the transfer film be used according to thelaser-assisted multi-chip transfer printing method.

The donor film may include a polydimethylsiloxane stamp (PDMS) film, apolyimide film including a dynamic release layer, an elastomericmicrostructure stamp film, or a shape memory polymer film.

By using the transfer film, the pixel unit (or the subpixel unit) isformed on the lower electrode through the laser-assisted multi-chiptransfer printing, thereby preventing a p-n junction of the ultra-thinLED element in the pixel unit (or the subpixel unit) from being reversedat a high rate when the pixel unit is formed through an existing inkjetprinting method or the like.

The plurality of ultra-thin LED elements simultaneously transferred ontothe lower electrode through a laser radiated through the same opening ofthe mask may form one pixel unit or one subpixel unit, and two or threesubpixel units may form one pixel unit.

The above-described high-resolution ultra-thin LED display of thepresent invention may have a resolving power of 450 PPI to 3,000 PPI,preferably a resolving power of 600 PPI to 2,000 PPI, and morepreferably a resolving power of 800 PPI to 2,000 PPI. As shown in FIG.1A, even when an existing micro-LED display having a resolving power of1,000 PPI or less is manufactured, there is a problem in that dark spotsoccur due to vacancies of LED elements, misalignment thereof, and thelike, but as shown in a schematic view of FIG. 1B, in the presentinvention, even when a display having a resolving power of 1,000 PPI to3,000 PPI is manufactured, a subpixel includes a plurality of LEDelements. Thus, it is possible to prevent the occurrence of defects suchas dark spots due to vacancies of the LED elements and misalignmentthereof.

In addition, the high-resolution ultra-thin LED display of the presentinvention may have a brightness of 100,000 cd/m² or more and a fastresponse time of 0.1 ms or less, and thus may be applied to variousdisplays, and preferably to displays of augmented reality (AR) orvirtual reality (VR) devices.

Hereinafter, exemplary embodiments will be described differentiating acase in which the ultra-thin-LED electrode assembly uses first typeultra-thin LED elements (dot type or disc type ultra-thin LED elements)and a case in which the ultra-thin-LED electrode assembly uses secondtype ultra-thin LED elements (micro-nanofin ultra-thin LED elements).

[First (Dot or Disc) Type Ultra-Thin LED Electrode Element and LEDElectrode Assembly]

An LED electrode assembly manufactured using first type ultra-thin LEDelements will now be described with reference to FIGS. 2A and 2B.

An ultra-thin LED electrode assembly 1000 according to an exemplaryembodiment of the present invention includes a lower electrode line 310including lower electrodes 311 and 312, a plurality of ultra-thin LEDelements 101 disposed on the lower electrodes 311 and 312, and an upperelectrode line 320 including upper electrodes 321 and 322 disposed incontact with upper portions of the ultra-thin LED elements 101.

First, prior to a detailed description of each component, electrodelines for allowing the ultra-thin LED elements to emit light will bedescribed.

The ultra-thin LED electrode assembly 1000 includes the upper electrodeline 320 and the lower electrode line 310 disposed at an upper side anda lower side to face each other with the ultra-thin LED elements 101interposed therebetween. Since the upper electrode line 320 and thelower electrode line 310 are not arranged in a horizontal direction, anelectrode design may be very simplified and more easily implemented bybreaking away from a complicated electrode line of a conventionalelectrode assembly using electric field induction, in which two types ofelectrodes implemented to have an ultra-thin thickness and width arearranged at intervals of a micro or nano unit within a planar surfacewith a limited area in the horizontal direction.

In particular, as shown in FIGS. 2A and 2B, irrespective of an electrodedesign of the lower electrode line 310, since the upper electrode line320 only needs to be disposed in electrical contact with upper surfacesof the disposed ultra-thin LED elements 101, there is an advantage inthat an electrode is very easily designed or implemented. In particular,although FIG. 2 illustrates that the upper electrodes 321 and 322 areindependent, since only one upper electrode may be implemented to be incontact with the upper surfaces of all the disposed ultra-thin LEDelements, there is an advantage in that an electrode line is implementedin a much more simplified form than in the related art.

In addition, the lower electrode line 310 and the upper electrode line320 may include the plurality of lower electrodes 311 and 312 and theplurality of upper electrodes 321 and 322, respectively, and since thenumbers, intervals, and arrangement shapes thereof may be appropriatelymodified in consideration of the size of an LED electrode assembly to beimplemented, the present invention is not particularly limited in thatrespect.

Furthermore, when the upper electrode line 320 is designed to be inelectrical contact with the upper portion of the ultra-thin LED element101 mounted on the lower electrode line 310, there is no limitation onthe number, arrangement, or the like thereof. However, when the lowerelectrode lines 310 are arranged in parallel in one direction as shownin FIG. 2A, the upper electrode line 320 may be arranged to beperpendicular to the one direction, and because such an electrodearrangement is an electrode arrangement widely used in the conventionaldisplay field, there is an advantage in that an electrode arrangementand control technology of the conventional display field can be usedwithout any change.

In addition, since the lower electrode line 310 and the upper electrodeline 320 may have a material, shape, width, and thickness of anelectrode used in a typical LED electrode assembly and may bemanufactured using a known method, the present invention is notspecifically limited in that respect. As an example, the lowerelectrodes 311 and 312 and the upper electrodes 321 and 322 may eachindependently be made of aluminum, chromium, gold, silver, copper,graphene, indium tin oxide (ITO), aluminum zinc oxide (AZO), or an alloythereof and may have a width of 0.1 μm to 50 μm and a thickness of 0.1μm to 100 μm, and may also be appropriately changed in consideration ofthe size or the like of a desired LED electrode assembly.

According to an exemplary embodiment of the present invention,arrangement regions S₁, S₂, S₃, and S₄ in which the ultra-thin LEDelements 101 are to be disposed may be formed on the lower electrodes311 and 312. The arrangement regions S₁, S₂, S₃, and S₄ may be veryvariously set according to the purpose and may be set a certain intervalfrom each other as shown in FIG. 2A, or an entire region on the lowerelectrodes 311 and 312 may become an arrangement region unlike what isshown in FIG. 2A.

Next, the ultra-thin LED element 101 disposed between the lowerelectrode line 310 and the upper electrode line 320 described above willbe described.

Referring to FIGS. 3 and 4 , the ultra-thin LED element 101 according toan exemplary embodiment of the present invention includes a firstconductive semiconductor layer 10, a photoactive layer 20, and a secondconductive semiconductor layer 30. In addition, the ultra-thin LEDelement 101 may further include an upper electrode layer 60 formed underthe first conductive semiconductor layer 10, a lower electrode layer 40formed on the second conductive semiconductor layer 30, and anarrangement guide layer 70 formed at an outermost side adjacent to thesecond conductive semiconductor layer 30.

The above-described layers are stacked in any one direction. In a dotLED, a ratio between a thickness in a stacking direction and a length ofa major axis in a cross section perpendicular to the stacking directionmay satisfy a range of 1:0.5 to 1:1.5, preferably a range of 1:0.8 to1:1.2, and more preferably a range of 1:0.9 to 1:1.1.

In addition, in a disc LED, a ratio between a thickness in a stackingdirection and a length of a major axis in a cross section perpendicularto the stacking direction may satisfy a range of 1:1.5 to 1:5.0,preferably a range of 1:1.5 to 1:3.0, and more preferably a range of1:1.5 to 1:2.5. Thus, when the ultra-thin LED elements are implementedinto an inkjet ink, the ultra-thin LED elements may exhibit excellentdispersibility in a dispersion medium and may be advantageous inmaintaining a dispersed state without precipitation for a long time.

In addition, due to such a geometrical structure suitable to be madeinto an ink, since there is no need for a separate additive formaintaining a dispersed state, there is an advantage in thatcontamination of the lower electrode line 310 or a circuit board due tothe separate additive can be prevented. Furthermore, when printing isperformed on the lower electrode line 310 using an ink including theultra-thin LED elements, conventional nanorod-type LED elements having alarge aspect ratio mostly lie down to be positioned on an electrode, andthe ultra-thin LED elements have an advantage in that a probability ofthe ultra-thin LED elements lying down when arranged on an electrode canreduced. In addition, it is possible to reduce a probability of aplurality of elements being assembled in different directions whenassembled on an electrode in a thickness direction thereof, in otherwords, a probability of a p-type conductive semiconductor layer and ann-type conductive semiconductor layer being assembled on a lowerelectrode in different directions, thereby reducing electrical leakagecaused due to a reverse arrangement and improving a lifetime. Here, thelength of the major axis is a diameter when a cross-sectional shape is acircular shape, a length of a major axis when a cross-sectional shape isan oval shape, and a length of the longest side when a cross-sectionalshape is a polygonal shape. Meanwhile, the above-described cross sectionis the largest surface of cross sections when the cross sections of theultra-thin LED element are not the same in a thickness directionthereof.

In addition, a ratio between a length of a minor axis and a length of amajor axis in the cross section may also satisfy a range of 1:0.5 to1:1.5, preferably a range of 1:0.8 to 1:1.2, and more preferably a rangeof 1:0.9 to 1:1.1, and thus it may be more advantageous in achieving theabove object of the present invention. Even if a ratio between athickness and a length of a major axis satisfies a range of 1:0.5 to1:1.5, when a ratio between a length of a minor axis and the length ofthe major axis in a cross section deviates from a range of 1:0.5 to1:1.5, since it is difficult for an LED element to maintain a dispersedstate in a dispersion medium for a long time, the LED element may beunsuitable to be made into an ink. In addition, in order to keep an LEDelement with such a geometry unsuitable for being made into an inkdispersed in a dispersion medium for a long time, an additive should befurther contained, and there is a risk of causing a problem ofcontaminating a driving electrode or a circuit board due to the use ofthe additive. Here, a length of a minor axis in a cross section is thelongest length among lengths of axes perpendicular to a major axis.

Meanwhile, in an ultra-thin LED element 101 shown in FIG. 3 , althoughcross sections of layers perpendicular to a stacking direction areillustrated as being the same size, the present invention is not limitedthereto, and sizes of the cross sections may be different sizesaccording to thicknesses.

In addition, a shape of the ultra-thin LED element 101 may be acylindrical shape as shown in FIG. 3 but is not limited thereto. Theshape of the ultra-thin LED element 101 may be an atypical shape havinga star-shaped surface as well as a polyhedral shape having a hexahedralsurface, an octahedral surface, or a decahedral surface.

According to an exemplary embodiment of the present invention, theultra-thin LED element 101 has a slow sedimentation rate when made intoan ink and thus has excellent dispersion retention performance formaintaining a dispersed state. Therefore, a maximum surface area of theultra-thin LED element 101 may be 25 μm² or less, preferably 9 μm² orless, more preferably 4 μm² or less, and still more preferably in arange of 0.1 μm² to 2.5 μm². Here, the maximum surface area is themaximum value among planar areas of the LED element. When the maximumsurface area exceeds 25 μm², a sedimentation rate may be high, and thusthere may be a risk of degrading dispersion retention performance, andthere may be a limitation in that the LED element is not suitable to bemade into an ink, a separate additive should be further added to makethe LED element into an ink, or a specific dispersion medium should beused.

According to an exemplary embodiment of the present invention, theultra-thin LED element 101 may have a thickness of 2.5 μm and morepreferably a thickness of 1.5 μm or less and thus may be more suitablefor maintaining a dispersed state for a long time when made into an ink.

However, when an LED element is implemented to be thin, a position atwhich electrons and holes combine deviates from the photoactive layer20, resulting in a decrease in luminous efficiency. In particular, whena large-area LED wafer is etched to implement the ultra-thin LEDelements, thicknesses of the first conductive semiconductor layer, thephotoactive layer, and the second conductive semiconductor layer arepreviously determined in a state of the LED wafer. In this case, inorder to achieve a certain level of luminous efficiency, only a part isetched to have a thickness different from the previously determinedthickness of each layer in the wafer to implement the ultra-thin LEDelements, and thus such a problem inevitably arises. Such a change in aposition at which electrons and holes combine is caused by a differencein velocity between electrons and holes moving through the conductivesemiconductor layers. For example, in an n-type GaN conductivesemiconductor layer, mobility of electrons is 200 cm²/Vs, but in ap-type GaN conductive semiconductor layer, mobility of holes is only 5cm²/Vs. Due to such an imbalance in electron-hole velocity, a positionat which electrons and holes combine may be changed according tothicknesses of the p-type GaN conductive semiconductor layer and then-type GaN conductive semiconductor layer and may deviate from thephotoactive layer.

When this is described with reference to FIG. 6 , in an LED element 200having a diameter of about 600 nm and including an n-type GaN conductivesemiconductor layer 210, a photoactive layer 220, and a p-type GaNconductive semiconductor layer 230 which are stacked, when a thicknessis designed such that the numbers of electrons and holes recombined at apoint A2 in the photoactive layer 220 are balanced in consideration ofelectron mobility of the n-type GaN conductive semiconductor layer 210and hole mobility of the p-type GaN conductive semiconductor layer 230,a thickness h of the n-type GaN conductive semiconductor layer 210should be inevitably thick, and thus, unless a thickness of the p-typeGaN conductive semiconductor layer 230 is implemented to be very thin, arod-type LED element is highly likely to be implemented. In other words,in the case of an LED element in which a thickness of each layer isdesigned such that a position at which the numbers of recombinedelectrons and holes are balanced is at the photoactive layer 220, as alength of a major axis in a cross section perpendicular to a thicknessdirection is decreased, an aspect ratio between the thickness of the LEDelement and the major axis of the cross section is inevitably furtherincreased. Thus, even if the numbers of holes and electrons recombinedin the photoactive layer are balanced, the LED element may beinappropriate to be implemented as an ink. In addition, when the n-typeGaN conductive semiconductor layer 210 is implemented to be thin so asto be suitable for being implemented into an ink, a position at whichthe numbers of recombined electrons and holes are balanced may bepositioned at any point A3 in the p-type GaN conductive semiconductorlayer 230, resulting in a decrease in luminous efficiency.

Accordingly, the ultra-thin LED element provided in an exemplaryembodiment of the present invention may have a geometric structuresuitable for being implemented into an ink and may further include anelectron delay layer adjacent to the n-type conductive semiconductorlayer in order to prevent a decrease in luminous efficiency by balancingthe numbers of holes and electrons recombined in the photoactive layer.When this is described with reference to FIG. 7 , assuming that a firstconductive semiconductor layer is an n-type conductive semiconductor, anultra-thin LED element 102 may include an electron delay layer 50 on afirst conductive semiconductor layer 10, and thus even when a thicknessof the first conductive semiconductor layer 10 is implemented to bethin, a decrease in luminous efficiency can be prevented. In addition,since the reduced thickness of the first conductive semiconductor layer10 reduces a probability of electrons being captured by surface defectswhile moving in a thickness direction of the first conductivesemiconductor layer 10, there is an advantage in that an emission losscan be minimized.

The electron delay layer 50 may include, for example, at least oneselected from among CdS, GaS, ZnS. CdSe, CaSe, ZnSe, CdTe, GaTe, SiC,ZnO, ZnMgO, SnO₂, TiO₂, In₂O₃, Ga₂O₃, S₁, poly(para-phenylene vinylene)or a derivative thereof, a poly(3-alkylthiophene), andpoly(paraphenylene). In addition, the electron delay layer 50 may have athickness of 1 nm to 100 nm, but the present invention is not limitedthereto. The thickness of the electron delay layer 50 may beappropriately changed in consideration of a material of the n-typeconductive semiconductor layer, a material of the electron delay layer,and the like.

Hereinafter, each layer of the ultra-thin LED element 101 and 102according to an exemplary embodiment of the present invention will bedescribed in detail.

Any one of the first conductive semiconductor layer 10 and the secondconductive semiconductor layer 30 may be an n-type semiconductor layer,and the other may be a p-type semiconductor layer. A known semiconductorlayer adopted in an LED may be used as the n-type semiconductor layerand the p-type semiconductor layer without limitation. As an example,the n-type semiconductor layer and the p-type semiconductor layer mayinclude III-V semiconductors referred to as III-nitride materials, inparticular, binary, ternary, and quaternary alloys of gallium, aluminum,indium, and nitrogen.

As an example, the first conductive semiconductor layer 10 may be ann-type semiconductor layer, and in this case, the n-type semiconductorlayer may include a semiconductor material having an empirical formulaof In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, atleast one selected from among InAlGaN, GaN, AlGaN, InGaN, AlN, and InN.The n-type semiconductor layer may be doped with a first conductivedopant (for example, Si, germanium (Ge), or tin (Sn)). According to anexemplary embodiment of the present invention, the first conductivesemiconductor layer 10 may have a thickness of 100 nm to 1,800 nm, butthe present invention is not limited thereto. The thickness of the firstconductive semiconductor layer 10 is preferably greater than or equal tothat of the second conductive semiconductor layer 30.

In addition, the second conductive semiconductor layer 30 may be ap-type semiconductor layer, and in this case, the p-type semiconductorlayer may include a semiconductor material having an empirical formulaof In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, atleast one selected from among InAlGaN, GaN, AlGaN, InGaN, AlN, and InN.The p-type semiconductor layer may be doped with a second conductivedopant (for example, magnesium (Mg)). According to an exemplaryembodiment of the present invention, the second conductive semiconductorlayer 30 may have a thickness of 50 nm to 150 nm, but the presentinvention is not limited thereto. The thickness of the second conductivesemiconductor layer 30 is preferably less than or equal to that of thefirst conductive semiconductor layer 10.

Also, the photoactive layer 20 positioned between the first conductivesemiconductor layer 10 and the second conductive semiconductor layer 30may be formed in a single or multi-quantum well structure. A photoactivelayer included in a typical LED element used for lighting, display, andthe like may be used as the photoactive layer 20 without limitation. Aclad layer (not shown) doped with a conductive dopant may be formedabove and/or under the photoactive layer 20 and may be implemented as anAlGaN laver or an InAlGaN layer. In addition, a material such as AlGaNor AlInGaN may be used for the photoactive layer 20. Regarding thephotoactive layer 20, when an electric field is applied to the element,electrons and holes move to the photoactive layer from the conductivesemiconductor layers positioned on and under the photoactive layer, andelectron-hole pairs are generated in the photoactive layer, therebyemitting light. According to an exemplary embodiment of the presentinvention, the photoactive layer 20 may have a thickness of 50 nm to 200nm, but the present invention is not limited thereto.

Meanwhile, the upper electrode layer 60 may be provided under the firstconductive semiconductor layer 10. Alternatively, the electron delaylayer 50 may be further provided between the first conductivesemiconductor layer 10 and the upper electrode layer 60. Meanwhile, thelower electrode layer 40 may be provided on the second conductivesemiconductor layer 30.

Electrode layers included in a typical LED element may be used as thelower electrode layer 40 and the upper electrode layer 60 withoutlimitation. The lower electrode layer 40 and the upper electrode layer60 may each independently be a single layer made of one selected fromchromium (Cr), titanium, (Ti), aluminum (Al), gold (Au), nickel (Ni),ITO, and an oxide or alloy thereof, a single layer in which two or morethereof are mixed, or multiple layers in which each of two or morematerials thereof constitutes a layer. As an example shown in FIG. 4 ,the ultra-thin LED element 102 may include a lower electrode layer 42 inwhich an ITO electrode laver 40 and a Ti/Au multi-layer 41 are stackedon the second conductive semiconductor layer 30. In addition, the lowerelectrode layer 40 and the upper electrode layer 60 may eachindependently have a thickness of 10 nm to 500 nm, but the presentinvention is not limited thereto.

Also, an arrangement guide layer, which is for erecting and arrangingthe ultra-thin LED element in a thickness direction thereof, may beformed at one side of the ultra-thin LED element in the thicknessdirection and one side or both sides of the arrangement regions S₁, S₂,S₃, and S₄ in which the ultra-thin LED element is to be disposed. Thearrangement guide layer guides the ultra-thin LED element 101 to moveonto desired regions on the lower electrodes 311 and 312, for example,onto the arrangement regions S₁, S₂, S₃, and S₄, and serves to erect andarrange the ultra-thin LED element 101 on the lower electrodes 311 and312. The arrangement guide layer may be formed at a side of theultra-thin LED element 101 and/or in desired regions on the lowerelectrodes 311 and 312, for example, in the arrangement regions S₁, S₂,S₃, and S₄.

In a case in which the arrangement guide layer is formed only on thelower electrodes 311 and 312, the arrangement guide layer may be a metalpart of the ultra-thin LED element 101, for example, a bonding layerthat can be chemically bonded to the lower electrode layer and/or theupper electrode layer. In this case, the bonding layer may be, forexample, a layer formed such that a thiol group is exposed to theoutside.

In addition, in a case in which the arrangement guide layer is formed inthe ultra-thin LED element 101, as shown in FIGS. 3 and 5A to 5C, thearrangement guide layer 70 may be further included on the lowerelectrode layer 40. A material of the arrangement guide layer 70 mayvary according to a specific guide and bonding method. For example, thearrangement guide layer 70 may be a charge layer having positive ornegative charges, specifically, a charge layer 71 having negativecharges as shown in FIG. 5A. Due to the charge layer 71, the ultra-thinLED element may be guided, erected, and assembled onto the lowerelectrode through an electrophoresis method which will be describedbelow. Alternatively, the arrangement guide layer may be a bonding layer72 as shown in FIG. 5 b , and functional groups exposed from the bondinglayer 72 may be chemically bonded to other functional groups provided onthe first electrode or may be bonded onto the lower electrode made of ametal material through chemical bonding, for example, adsorption. Inaddition, the arrangement guide layer 70 may be a magnetic layer 73 asshown in FIG. 5C, and the magnetic layer 73 may be assembled on thelower electrodes 311 and 312 by a magnetic field.

Meanwhile, when the arrangement guide layer 70 provided in theultra-thin LED element is the charge layer 71, a charge layer that hascharges opposite to those of the charge layer 71 provided in theultra-thin LED element may be provided in the arrangement region on thelower electrodes 311 and 312, and thus there is an advantage in that theultra-thin LED element can be better guided to the arrangement regionand simultaneously the ultra-thin LED element can be better erected andguided. The charge layer is not limited as long as the charge layer ismade of a material having positive or negative charges and is alsosuitable for forming a layer or a film.

In addition, even when the arrangement guide layer 70 provided in theultra-thin LED element is the magnetic layer 73, a magnetic layer may befurther included in the arrangement region on the lower electrodes 311and 312, and thus there is an advantage in that the ultra-thin LEDelement can be better guided to the arrangement region andsimultaneously the ultra-thin LED element can be better erected andguided. The magnetic layer 73 may be made of a ferromagnetic material ora paramagnetic material.

Meanwhile, in FIGS. 3 and 4 , although a position of the arrangementguide layer 70 is illustrated to be positioned on the lower electrodelayer 40, the present invention is not limited thereto, and thearrangement guide layer 70 may be disposed to be positioned on the upperelectrode layer 60. In other words, the arrangement guide layer 70 maybe provided in the ultra-thin LED element to be provided at any one sideof the ultra-thin LED element in the thickness direction, that is,become an uppermost layer or a lowermost layer.

In addition, the ultra-thin LED element 101 may further include aprotective film 80 which surrounds a side surface of the element when itis assumed that a surface parallel to a stacking direction is the sidesurface. The protective film 80 performs a function of protectingsurfaces of the first conductive semiconductor layer 10, the photoactivelayer 20, and the second conductive semiconductor layer 30. In addition,as in a manufacturing method of an ultra-thin LED element to bedescribed below, the protective film 80 may perform a function ofprotecting the first conductive semiconductor layer 10 in a process ofetching an LED wafer in a thickness direction thereof and thenseparating a plurality of LED pillars.

The protective film 80 may include, for example, at least one selectedfrom among silicon nitride (Si₃N₄), silicon dioxide (SiO₂), aluminumoxide (Al₂O₃), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), yttriumoxide (Y₂O₃), titanium dioxide (TiO₂), aluminum nitride (AlN) andgallium nitride (GaN). The protective film 80 may have a thickness of 5nm to 100 nm and more preferably a thickness of 30 nm to 100 nm and thusmay be advantageous in protecting the first conductive semiconductorlayer 10 in the process of separating the LED pillars which will bedescribed below.

Meanwhile, as shown in FIG. 8 , an ultra-thin LED element 103 accordingto an exemplary embodiment of the present invention may include aprotective film 80′, which includes a hole pushing film 81 whichsurrounds an exposed side surface of a second conductive semiconductorlayer 30 or the exposed side surface of the second conductivesemiconductor layer 30 and an exposed side surface of at least a portionof a photoactive layer 20 to move holes at a side of the exposed sidesurface toward the center and an electron pushing film 82 whichsurrounds an exposed side surface of a first conductive semiconductorlayer 10 to move electrons at a side of the exposed side surface towardthe center, in order to have improved luminous efficiency in addition toa protective function as a protective film.

Some of charges moving from the first conductive semiconductor layer 10to the photoactive layer 20 and some of holes moving from the secondconductive semiconductor layer 30 to the photoactive layer 20 may movealong a side surface. In this case, electrons or holes are quenched dueto defects present on the surface, and thus there is a risk of degradingluminous efficiency. In this case, even if a protective film isprovided, there is a problem that quenching is unavoidable due todefects occurring on a surface of an element before the protective filmis provided. However, when the protective film 80′ includes the holepushing film 81 and the electron pushing film 82, since electrons andholes are concentrated toward the center of the element and are guidedand moved toward the photoactive layer, there is an advantage in that itis possible to prevent a loss of luminous efficiency due to surfacedefects even if there are defects on the surface of the element beforethe protective film is formed.

The hole pushing film 81 may include, for example, at least one selectedfrom the group consisting of AlN_(x), ZrO₂, MoO, Sc₂O₃, La₂O₃, MgO,Y₂O₃, Al₂O₃, Ga₂O₃, TiO₂, ZnS, Ta₂O₅, and n-MoS₂. The electron pushingfilm 82 may include at least one selected from the group consisting ofAl₂O₃, HfO₂, SiN_(x), SiO₂, ZrO₂, Sc₂O₃, AlN_(x), and Ga₂O₃.

In addition, as shown in FIG. 8 , when the ultra-thin LED elementincludes both the hole pushing film 81 and the electron pushing film 82,the electron pushing film 82 may be provided as an outermost film whichsurrounds side surfaces of the first conductive semiconductor layer 10,the photoactive layer 20, and the second conductive semiconductor layer30.

In addition, the hole pushing film 81 and the electron pushing film 82may each independently have a thickness of 1 nm to 50 nm.

Meanwhile, the first conductive semiconductor layer 10, the photoactivelayer 20, and the second conductive semiconductor layer 30 of theabove-described ultra-thin LED element may be included as minimalcomponents of the ultra-thin LED element, and another phosphor layer, aquantum dot layer, another active layer, a semiconductor layer, a holeblock layer, and/or an electrode layer may be further includedabove/under each layer.

The ultra-thin LED electrode assembly 1000 described above may bemanufactured through a manufacturing method, which will be describedbelow, when manufactured through an inkjet printing method.Specifically, the ultra-thin LED electrode assembly 1000 may bemanufactured by performing operation 1 of providing a lower electrodeline including lower electrodes, operation 2 of forming a plurality ofpixel units on the lower electrodes, and operation 3 of forming an upperelectrode line, which includes upper electrodes, to be electricallyconnected to an opposite side of an ultra-thin LED element opposite toone side of the ultra-thin LED element assembled on the lower electrode.

In operation 2, operation 2-1 of processing an ink composition includinga plurality of ultra-thin LED elements on the lower electrodes, andoperation 2-2 of erecting the ultra-thin LED elements in a thicknessdirection thereof to assemble the ultra-thin LED elements on the lowerelectrodes may also be performed.

The content described above for the ultra-thin LED electrode assembly1000 will be omitted below in description of a manufacturing method.

As operation 1 according to the present invention, an operation ofproviding a lower electrode line 310 including lower electrodes 311 and312 is performed.

The lower electrodes 311 and 312 may be implemented as various knownelectrode patterns through a known method, and the present invention isnot particularly limited in that respect. As an example shown in FIG. 1, the plurality of lower electrodes 311 and 312 may be implemented aspatterns which are spaced a certain interval from each other andarranged in parallel. The lower electrodes 311 and 312 may be formed ona substrate 400 (or a base substrate), and the substrate 400 may be, forexample, any one of a glass substrate, a quartz substrate, a sapphiresubstrate, a plastic substrate, and a flexible polymer film that isbendable. As another example, the substrate 400 may be transparent.However, the present invention is not limited to the listed types, andany type of a substrate capable of typically forming an electrode may beused.

An area of the substrate 400 (or the base substrate) is not limited andmay be changed in consideration of an area of the lower electrodes 311and 312 formed on the substrate 400. In addition, the substrate 400 mayhave a thickness of 100 μm to 1 mm, but the present invention is notlimited thereto.

Next, in operation 2-1 of operation 2 according to the presentinvention, the ultra-thin LED element includes a first conductivesemiconductor layer 10, a photoactive layer 20, and a second conductivesemiconductor layer 30 which are stacked. A ratio between a thickness ina stacking direction and a length of a major axis in a cross sectionperpendicular to the stacking direction may be in a range of 1:0.5 to1:1.5 or 1:1.5 to 1:5.0. An operation of processing the ink compositionincluding the plurality of the ultra-thin LED elements 101 on the lowerelectrodes 311 and 312 is performed.

The ultra-thin LED elements 101 are provided as an ink composition inwhich the plurality ultra-thin LED elements 101 are made into an ink. Anultra-thin-film LED element assembly 100 including the plurality ofultra-thin-film LED elements 101 may be manufactured throughmanufacturing method 1 shown in FIGS. 9 and 10 or manufacturing method 2shown in FIG. 11 . Manufacturing method 1 may be usefully selected whenan n-type III-nitride semiconductor layer is a doped n-type III-nitridesemiconductor layer, and manufacturing method 2 may be useful when then-type III-nitride semiconductor layer is not doped.

Manufacturing methods 1 and 2 are common from an operation of providingan LED wafer 100 a to an operation of manufacturing a wafer including aplurality of LED structures (100 h in FIG. 9 or 100 h in FIG. 11 ) andare different in a method of separating the formed LED structures fromthe wafer. The operation of providing the LED wafer 100 a to theoperation of manufacturing the wafer including the plurality of LEDstructures (100 h in FIG. 9 or 100 h in FIG. 11 ) will be describedthrough manufacturing method 1.

First, manufacturing method 1 will be described with reference to FIG. 9.

Manufacturing method 1 may include operation A of providing an LED wafer100 a (see FIG. 9A), operation B of patterning an upper portion of theLED wafer 100 a such that a planar surface, which is perpendicular to adirection in which layers are stacked in an individual LED structure,has a desired shape and size (see FIGS. 9B and 9C), and then verticallyperforming etching down to at least a partial thickness of a conductivesemiconductor layer 10 to form a plurality of LED structures (see FIG.9D to 9H), operation C of forming a protective film to surround anexposed surface of each of the plurality of LED structures and expose anupper surface of a first portion between the adjacent LED structures tothe outside (see FIGS. 9I to 9J), operation D of immersing the LED waferin an electrolyte to then electrically connect the LED wafer to any oneterminal of a power supply and electrically connect the other terminalof the power supply to an electrode immersed in the electrolyte, andthen applying power to form a plurality of pores in the first portion(see FIGS. 9K and 9E), and operation E of applying ultrasonic waves tothe LED wafer to separate the plurality of LED structures from the firstportion in which the plurality of pores are formed (see FIG. 9O).

As the LED wafer 100 a provided in operation A, a commercially availableLED wafer may be used without limitation. As an example, the LED wafer100 a may include a substrate 1, a first conductive semiconductor layer10, a photoactive layer 20, and a second conductive semiconductor layer30. In this case, the first conductive semiconductor layer 10 may be ann-type III-nitride semiconductor layer, and the second conductivesemiconductor layer 30 may be a p-type III-nitride semiconductor layer.In addition, since the LED structures remaining on the LED wafer afterthe n-type III-nitride semiconductor layer is etched to a desiredthickness can be separated through operations C to E, a thickness of then-type III-nitride semiconductor layer in the LED wafer is likewise notlimited, and the presence or absence of a separate sacrificial layer maynot be considered when a wafer is selected.

Furthermore, each layer in the LED wafer 100 a may have a c-planecrystal structure.

In addition, the LED wafer 100 a may have been subjected to a cleaningprocess, and since a typical wafer cleaning solution and cleaningprocess may be appropriately adopted for the cleaning process, thepresent invention is not particularly limited in that respect. Thecleaning solution may be, for example, isopropyl alcohol, acetone, or ahydrochloric acid but is not limited thereto.

Next, before operation B is performed, an operation of forming a lowerelectrode layer 40 on the second conductive semiconductor layer 30 whichis the p-type III-nitride semiconductor layer may be performed. Thelower electrode layer 40 may be formed through a typical method offorming an electrode on a semiconductor layer, for example, through adeposition process using sputtering. A material of the lower electrodelayer 40 may be, for example, ITO as described above, and the lowerelectrode layer 40 may be formed to have a thickness of about 150 nm.The lower electrode layer 40 may be further subjected to a rapid thermalannealing (RTA) process after the deposition process and may beprocessed, for example, at a temperature of 600° C. for 10 minutes, butsince the RTA may be appropriately adjusted in consideration of thethickness, material, and the like of the electrode layer, the presentinvention is not particularly limited in that respect.

Next, in operation B, the upper portion of the LED wafer may bepatterned such that the planar surface perpendicular to the direction inwhich the layers are stacked in each LED structure has the desired shapeand size (see FIGS. 9B and 9C). Specifically, a mask pattern layer maybe formed on an upper surface of the lower electrode layer 40, and themask pattern layer may be formed using a known method and a materialused for etching an LED wafer etching. A pattern of the pattern layermay be formed by appropriately applying a typical photolithographymethod, a nanoimprinting method, or the like.

As an example shown in FIG. 9F, the mask pattern layer may be a stack ofa first mask layer 2, a second mask layer 3, and a resin pattern layer4′ of which certain patterns are formed on the lower electrode layer 40.To briefly described a method of forming the mask pattern layer, as anexample, after the first mask layer 2 and the second mask layer 3 areformed on the lower electrode layer 40 through deposition, and a resinlayer 4 using which the resin pattern layer 4′ is formed is formed onthe second mask layer 3 (see FIGS. 9B and 9C), a residual resin portion4 a of the resin layer 4 is removed through a typical method such as areactive ion etching (RIE) method (see FIG. 9D), and then the secondmask layer 3 and the first mask layer 2 are sequentially etched along apattern of the resin pattern layer 4′ (see FIGS. 9E and 9F), therebyforming the mask pattern layer. In this case, the first mask layer 2 maybe made of, for example, silicon dioxide, the second mask layer 3 may bea metal layer of aluminum, nickel, or the like, and each of the firstmask layer 2 and the second mask layer 3 may be etched using RIE andinductively coupled plasma (ICP). Meanwhile, when the first mask layer 2is etched, the resin pattern layer 4′ may also be removed (see 100F).

In addition, the resin layer 4 using which the resin pattern layer 4′ isformed may be formed through a nanoimprinting method. After a moldcorresponding to a certain desired pattern template is manufactured, aresin is processed in the mold to form the resin layer, and then theresin layer 4 is transferred to be positioned on a wafer stack 100 b inwhich the first mask layer 2 and the second mask layer 3 are formed onthe lower electrode layer 40 to then remove the mold, therebyimplementing a wafer stack 100 c in which the resin layer 4 is formed.

Meanwhile, although a method of forming a pattern through ananoimprinting method has been described, the present invention is notlimited thereto, and a pattern may be formed through photolithographyusing a known photosensitive material or may be formed through knownlaser interference lithography, electron beam lithography, or the like.

Thereafter, as shown in FIG. 9G, along the patterns of the mask patternlayers 2 and 3 formed on the lower electrode layer 40, etching may beperformed down to a partial thickness of the first conductivesemiconductor layer 10, which is the n-type III-nitride semiconductorlayer, in a direction perpendicular to a surface of an LED wafer 100 fto manufacture an LED wafer 100 g on which the LED structures areformed. In this case, the etching may be performed through a typical dryetching method such as an ICP method and a potassium hydroxide(KOH)/anisotropic tetramethylammonium hydroxide (TMAH) wet etchingmethod. In such an etching process, the second mask layer 3 made of Alconstituting the mask pattern layer may be removed, and then the firstmask layer 2 made of silicon dioxide constituting the mask pattern layerpresent on the lower electrode layer 40 of each LED structure in the LEDwafer 100 g may be removed to manufacture an LED wafer 100 h on whichthe plurality of LED structures are formed.

Next, as operation C, an operation of forming a protective film 80 a toa certain thickness to surround the exposed surface of each of theplurality of LED structures in the LED wafer 100 h on which theplurality of LED structures are formed and expose an upper surface S1 ofa first portion a between the adjacent LED structures to the outside isperformed (see FIGS. 9I to 9J). The protective film 80 a may be forpreventing damage to the LED structure due to the performing ofoperation D which will be described below. In addition, when theprotective film 80 a continues to remain on a side surface of the LEDstructure separated from the LED wafer, the protective film 80 a mayalso perform a function of protecting the side surface of theindividually separated LED structure from external stimuli.

When operations C to E are described with reference to FIG. 10 ,operation C may be performed through operation C-1 of depositing aprotective film material on the LED wafer 100 h on which the pluralityof LED structures are formed and forming the protective film 80 a to acertain thickness to surround the exposed surface of each of theplurality of LED structures, and operation C-2 of removing theprotective film deposited on the upper surface S1 of the first portion abetween the adjacent LED structures to expose the upper surface S1 ofthe first portion a between the LED structures to the outside.

Operation C-1 is an operation of depositing the protective film materialon the LED wafer 100 h on which the plurality of LED structures areformed (see FIG. 10A). In this case, the protective film material may bea known material that is not chemically attacked by an electrolyte of anoperation which will be described below. As an example, theabove-described materials of a protective film 80 can be used withoutlimitation. As an example, the protective film material may include atleast one selected from among silicon nitride (Si₃N₄), silicon dioxide(SiO₂), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), zirconium oxide(ZrO₂), yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃), scandium oxide(Sc₂O₃), titanium dioxide (TiO₂), aluminum nitride (AlN), and galliumnitride (GaN). In addition, the protective film 80 a formed throughdeposition of the protective film material may have a thickness of 5 nmto 100 nm and more preferably a thickness of 30 nm to 100 nm. When thethickness of the protective film 80 a is less than 5 nm, it may bedifficult to prevent the LED structure from being attacked by anelectrolyte in operation D which will be described below. When thethickness of the protective film 80 a exceeds 100 nm, there may beproblems in that manufacturing costs are increased and the LEDstructures are connected.

Next, operation C-2 is an operation of removing the protective filmdeposited on the upper surface S1 of the first portion a between theadjacent LED structures to expose the upper surface S1 of the firstportion a between the LED structures to the outside (see FIG. 10B). Dueto the performing of operation C-1, the protective film material mayalso be deposited on the upper surface S1 of the first portion a betweenthe adjacent LED structures.

Accordingly, an electrolyte may not come into contact with the firstconductive semiconductor layer 10 that is the n-type III-nitridesemiconductor, and thus desired pores may not be formed in the firstportion a. Accordingly, the operation of removing the protective filmmaterial applied on the upper surface S1 of the first part a to exposethe upper surface S1 to the outside is performed. In this case, theprotective film material may be removed through a known dry or wetetching method in consideration of the protective film material.

Meanwhile, according to an exemplary embodiment of the presentinvention, the protective film 80 a formed in operation C is a temporaryprotective film to prevent damage to the LED structure due to theperforming of operation C. An operation of removing the temporaryprotective film and then forming a surface protective film surroundingthe side surface of the LED structure may be further included betweenoperations D and E. That is, as shown in FIG. 9 , in operation 3, aprotective film 5′ may be provided only as a temporary protective filmfor preventing damage to the LED structure in operation 4 (see FIGS. 9Ito 9K), and after the protective film 5′ is removed before operation 5is performed, the surface protective film 80 for performing a functionof preventing damage to the surface of the LED structure may be formedto cover the side surface of the LED structure (see FIG. 9M).

Meanwhile, in some exemplary embodiments as shown in FIG. 9 , althoughthe protective film needs to be formed twice, the formation of theprotective film may be selected in consideration of the planar shape andsize of the manufactured LED structure and an interval between the LEDstructures. In addition, when operation D, which will be describedbelow, is performed, the protection film may be partially attacked. Whenthe attacked protective film is left on the finally obtained individualLED structure and is used as a surface protective film, there may becases in which it may be difficult to properly perform a surfaceprotection function, and thus in some cases, it may be advantageous toprovide a protective film again after removing the protective filmsubjected to operation D.

To described the manufacturing process shown in FIG. 9 , after atemporary protective film material 5 is deposited on the LED wafer 100 hon which the plurality of LED structures are formed (see FIG. 9I), theprotective film 5′, which is a temporary protective film for protectingthe side surfaces and upper portions of the plurality of LED structures,may be formed by etching the temporary protective film material 5deposited on the upper surface SI of the first portion a of the firstconductive semiconductor layer 10 which is the doped n-type III-nitridesemiconductor layer between the adjacent LED structures of an LED wafer100 i on which the protective film material 5 is deposited. Thereafter,after operation D, which will be described below, is performed (see FIG.9K), the protective film 5′ may be removed through etching (see FIG.9I), a protective film material may be deposited on an LED wafer 100 las a surface protective film for protecting the surface of the LEDstructure, and then the protective film material formed on each of theED structures may be removed to form the protective film 80 surroundingthe side surface of the LED structure (see FIG. 9M). In this case, theprotective film material formed on the upper part of the LED structuremay be removed together with the protective film material deposited onthe upper surface S1 of the first portion a of the first conductivesemiconductor layer 10 which is the doped n-type III-nitridesemiconductor layer between the adjacent LED structures of an LED wafer100 m.

Thus, in operation 3 which will be described, a bubble-forming solventcan come into contact with the upper surface S1 of the first portion a,and bubbles generated through ultrasonic waves may penetrate into poresP formed in the first portion a, thereby separating the LED structurethrough the bubbles.

Meanwhile, descriptions of the temporary protective film material andthe surface protective film material are the same as the descriptions ofthe materials of the above-described protective film. The thickness ofthe implemented thin film may also be implemented within the thicknessrange of the above-described protective film.

Next, as operation D of manufacturing method 1, an operation ofimmersing the LED wafer in the electrolyte to electrically connect theLED wafer to any one terminal of the power supply and electricallyconnect the other terminal of the power supply to the electrode immersedin the electrolyte, and then applying power to form the plurality ofpores in the first portion is performed.

Specifically, referring to FIG. 10 , an LED wafer 100 h 2 on which theprotective film 80 a is formed may be electrically connected to any oneterminal of the power supply, for example, an anode, the electrodeimmersed in the electrolyte may be electrically connected to the otherterminal of the power supply, for example, a cathode, and then power maybe applied to manufacture an LED wafer 100 h 3 in which the plurality ofpores P are formed in the first portion a of the first conductivesemiconductor layer 10 which is the doped n-type III-nitridesemiconductor. In this case, the pores P may start to be formed from theupper surface SL, which is in direct contact with the electrolyte, ofthe first portion a of the first conductive semiconductor layer 10,which is the doped n-type III-nitride semiconductor, and may be formedin a thickness direction and a lateral direction of a side of the firstportion a corresponding to a lower portion of each of the LEDstructures.

The electrolyte used in operation D may include at least one oxygen acidselected from the group consisting of oxalic acid, phosphoric acid,sulfurous acid, sulfuric acid, carbonic acid, acetic acid, chlorousacid, chloric acid, bromic acid, nitrous acid, and nitric acid, and morepreferably, oxalic acid may be used. Thus, there is an advantage in thatdamage to the first conductive semiconductor layer can be minimized. Inaddition, the electrode may be made of platinum (Pt), carbon (C), nickel(Ni), gold (Au), or the like and may be, for example, a platinumelectrode. In addition, in operation D, a voltage of 3 V or more may beapplied as the power for 1 minute to 24 hours, and thus the pores P maybe smoothly formed down to the side of the first portion a correspondingto the lower portion of each of the plurality of LED structures, therebymore easily separating the LED structure from the wafer throughoperation E. More preferably, the voltage may be 10 V or more, and morepreferably, a voltage of 30 V or less may be applied.

When a voltage of less than 3 V is applied, even if an application timeof power is increased, the pores are not smoothly formed in the side ofthe first portion a corresponding to the lower portion of each LEDstructure, and thus it is difficult to separate the LED structurethrough operation E which will be described below, or even if the LEDstructure is separated, shapes of separated cross sections of theplurality of LED structures may be different, and thus it may bedifficult for the plurality of LED structures to exhibit uniformcharacteristics. In addition, when a voltage exceeding 30 V is applied,the pores may be formed down to a second portion b which is a lower endportion of the LED structure and continue to the first portion a of thedoped n-type III-nitride semiconductor layer, thereby causingdegradation in light emitting characteristic. In addition, in operationE which will be described below, it is preferable that the LED structureis separated at a boundary point between the second portion b and thefirst portion a of the doped n-type III-nitride semiconductor layer.However, due to the pores formed in a side of the second portion b,separation may occur at any point of the side of the second portion bbeyond the boundary point, and thus there is a risk that an LEDstructure, which has an n-type semiconductor layer that is thinner thanan initially designed n-type semiconductor layer, may be obtained. Inaddition, similarly to an effect according to a magnitude of a voltage,when an application time of power is also increased, there is a riskthat pores may be formed down to the second portion b other than anintended portion, and on the other hand, when the application time isdecreased, pores may not be smoothly formed, and thus it may bedifficult to separate the LED structure.

After operation D and before operation E which will be described below,in order to enable electrical connection to a side of the lowerelectrode layer 40 after the LED structure is separated from the wafer,an operation of manufacturing an LED wafer 100 h 4, from which aprotective film of the protective film 80 a formed on an upper surfaceof each LED structure is removed, may be further performed. In addition,since only the protective film formed on the upper surface of the LEDstructure is removed, the protective film 80 formed on the side surfaceof the LED structure may remain and thus may perform a function ofprotecting the side surface of the LED structure from the outside.

In addition, after operation D and before operation E which will bedescribed below, an operation of forming another layer on the lowerelectrode layer 40 of the LED structure may be further performed, andanother layer may be, for example, a Ti/Au composite layer or anarrangement guide layer 70 which may be further formed using a lowerelectrode layer material on the lower electrode layer 40 which is an ITOlayer (see FIG. 9N).

Next, as operation E according to manufacturing method 1, an operationof applying ultrasonic waves to the LED wafer 100 h 4 to separate theplurality of LED structures from the first portion a in which theplurality of pores P are formed is performed. In this case, ultrasonicwaves may be directly applied to the LED wafer 100 h 4 in which thepores are formed or indirectly applied by immersing the LED wafer 100 h4 in which the pores are formed, in a solvent. However, in a method ofcollapsing the pores P of the first portion a using a physical externalforce caused by the ultrasonic wave itself, the collapse of the pores isnot smooth, and when the pores are excessively formed to facilitate thecollapse, there is a risk of pores being formed down to the secondportion b of the LED structure, which may cause a side effect oflowering the quality of the LED structure.

Thus, according to an exemplary embodiment of the present invention,operation E may be performed using a sonochemistry method. Specifically,after the LED wafer 100 h ₄ is immersed in a bubble-forming solution 76(or solvent), ultrasonic waves are applied to the bubble-formingsolution 76 (or solvent) to collapse bubbles through energy generatedwhen generated and grown bubbles burst in the pores by a sonochemicalmechanism, thereby separating the plurality of LED structures. Indetail, ultrasonic waves alternately generate a relatively high pressurepart and a relatively low pressure part in a travel direction of soundwaves, and generated bubbles pass through the high pressure part and thelow pressure part to repeatedly compress and expand and grow intobubbles with a higher temperature and pressure and then collapse. Thebubble becomes a local hot spot that generates a high temperature of4,000K level and a high pressure of an atmospheric pressure level of1,000, and pores generated in the LED wafer are collapsed using suchenergy, thereby separating the LED structure from the wafer. After all,ultrasonic waves generate and grow bubbles in the bubble-formingsolution (or solvent) and perform only a function of moving andpenetrating the generated bubbles into the pores P of the first portiona. Then, through a pore collapse mechanism in which the pores P arecollapsed by an external force generated when bubbles, which penetrateinto the pores P and are in an unstable state with a high temperatureand pressure, burst, the plurality of LED structures can be easilyseparated from the LED wafer, thereby obtaining an LED assembly 100′including a plurality of ultra-thin LED elements 101′.

As the bubble-forming solution 76 (or solvent), a solution (or solvent),which can generate bubbles when ultrasonic waves are applied and can begrown to have high pressure and temperature, may be used withoutlimitation. Preferably, a bubble-forming solution (or solvent) with avapor pressure of 100 mmHg (20° C.) or less, as another example, a vaporpressure of 80 mmHg (20° C.) or less, 60 mmHg or less (20° C.), 50 mmHgor less (20° C.), 40 mmHg or less (20° C.), 30 mmHg or less (20° C.) orless. 20 mmHg or less (20° C.), or 10 mmHg or less (20° C.) or less, maybe used. When a solvent having a vapor pressure exceeding 100 mmHg (20°C.) is used, separation may not occur properly within a short time, andthus there may be a risk of a manufacturing time increasing andproduction costs increasing. The bubble-forming solution 76 satisfyingsuch physical properties may be, for example, at least one selected fromthe group consisting of gamma-butyllactone, propylene glycol methylether acetate, methyl pyrrolidone, and 2-methoxyethanol. Meanwhile, asolution (or solvent) having a vapor pressure of 100 mmHg at roomtemperature, for example, 20° C., may be used as the bubble-formingsolution (or solvent), but by adjusting conditions for performingoperation E, a vapor pressure of the bubble-forming solution (orsolvent) may be adjusted to 100 mmHg or less in the conditions (forexample, a low temperature condition) to perform operation E. In thiscase, a limitation on types of usable solvents may become wider, and asan example, a solvent such as water, acetone, chloroform, or alcohol maybe used.

In addition, a wavelength of ultrasonic waves applied in operation E maybe applied at a frequency at which, when bubbles are collapsed, thebubbles can be grown and collapsed to become regions that can causesonochemistry, specifically, local hot spots that generate high pressureand temperature. As an example, the wavelength may be in a range of 20kHz to 2 MHz, and an application time of the applied ultrasonic wavesmay be in a range of 1 minute to 24 hours, thereby making it easy toseparate the LED structure from the LED wafer. Even if the wavelength ofthe applied ultrasonic waves falls within this range, when an intensitythereof is low or the application time is short, there is a risk of LEDstructures not separated from the LED wafer being present, or the numberof LED structures not separated from the LED wafer increasing. Inaddition, when the intensity of the applied ultrasonic waves is high orthe application time is long, there is a risk of damage to the LEDstructure.

In each of the plurality of LED structures separated through theformation of pores in operation D and the application of ultrasonicwaves in operation E, pores may be formed in a portion of the firstconductive semiconductor layer (n-type conductive semiconductor layer).

Meanwhile, before operation E is performed, in order to form an upperelectrode layer 60 on the first conductive semiconductor layer 10, thatis, in order to form another layer, for example, the upper electrodelayer 60 or an electron delay layer (not shown) on the first conductivesemiconductor layer 10, an operation of attaching a support film 9 ontoan LED wafer 100 n (see FIG. 9O) may be further performed, and thenoperation E may be performed to separate the plurality of LED structuresin a state in which the support film 9 is attached (see FIG. 9P). Afterthat, the upper electrode layer 60 may be formed on the plurality of LEDstructures through a known method such as a deposition method in a statein which the support film 9 is attached (see FIG. 9Q), and then when thesupport film is removed, an aggregate 100 of a plurality of ultra-thinLED elements 101 may be obtained.

Next, a method of manufacturing an ultra-thin LED element throughmanufacturing method 2 will be described with reference to FIG. 11 .

As described above, forming an LED wafer 100 h on which a plurality ofLED structures are formed from an LED wafer is the same as inmanufacturing method 1. Thereafter, manufacturing method 2 may beperformed through operation i of forming an insulating film 8 to coverexposed side surfaces of the plurality of LED structures in the LEDwafer 100 h on which the plurality of LED structures are formed (seeFIG. 11B), operation ii of removing a portion of an insulating filmformed on a first conductive semiconductor layer 10 to expose an uppersurface S1 of the first conductive semiconductor layer 10 between theadjacent LED structures (FIG. 11C), operation iii of further etching thefirst conductive semiconductor layer 10 in a thickness direction thereofthrough the exposed upper surface S1 of the first conductivesemiconductor layer and forming a portion of the first conductivesemiconductor layer of which a side surface is exposed by as much as acertain thickness in a downward direction of the first conductivesemiconductor layer of an LED pillar on which an insulating film 8′ isformed (see FIG. 11C), operation iv of etching the portion of the firstconductive semiconductor layer, of which the side surface is exposed,from both side surfaces thereof toward a center thereof (see FIG. 11D),operation v of removing the insulating film 8 (see FIG. 11E), operationvi of forming a protective film 80 on the side surfaces of the pluralityof LED structures (FIG. 11F), operation vii of removing the protectivefilm formed on the plurality of LED structures to expose a lowerelectrode layer 40 (see FIG. 11G), operation viii of forming anarrangement guide layer 70 on the lower electrode layer 40 (see FIG.11H), and operation ix of separating the plurality of LED structuresfrom the LED wafer to manufacture an ultra-thin LED aggregate 100″including a plurality of ultra-thin LED elements 100″. Meanwhile,manufacturing method 2 described above may be performed by appropriatelyusing a known method of manufacturing an LED element, for detaileddescription thereof, application No. 2020-0050884 by the inventor of thepresent invention is herein incorporated by reference in its entirety,and in the present invention, detailed description of each operation ofmanufacturing method 2 is omitted.

In this case, the separation of the plurality of LED structures inoperation ix may be performed through cutting using a cutting mechanismor detachment using an adhesive film.

Meanwhile, as described above with reference to FIG. 8 , as a protectivefilm, a protective film 80′ including a hole pushing film 81 and anelectron pushing film 82 for improving luminous efficiency may beformed, and a manufacturing method thereof will be described withreference to FIG. 12 .

A difference from the description with reference with FIGS. 9 to 11 isthat, when etching is vertically performed, a portion of a firstconductive semiconductor layer 10 which is an n-type semiconductor isnot etched, the etching is primarily performed only down to a secondconductive semiconductor layer 30, a portion of a photoactive layer 20,or the photoactive layer 20 (see FIG. 12A), then etching is secondarilyperformed down to a partial thickness of the first conductivesemiconductor layer 10 (see FIG. 12C), and a process of depositing afilm material and removing the film material between a plurality of LEDstructures is performed twice (FIGS. 12B, 12D, and 12E).

Specifically, when an LED wafer is vertically etched, a portion of thefirst conductive semiconductor layer 10 which is the n-typesemiconductor is not etched, the LED wafer is primarily etched only downto the second conductive semiconductor layer 30, the second conductivesemiconductor layer 30 and a portion of the photoactive layer 20, or thephotoactive layer 20 (see FIG. 12A), and then, after a hole pushing filmmaterial 81 a is deposited (see FIG. 12B), a process of removing thehole pushing film material formed between the LED structures isperformed. Thereafter, the LED wafer may be secondarily etched again toa certain thickness of the first conductive semiconductor layer 10 (FIG.12C), an electron pushing film material 82 a may be deposited on the LEDstructure in which the hole pushing film 81 b is formed (see FIG. 12D),and then a process of removing the electron pushing film material formedin a space S1 between the LED structures (see FIG. 12E) may beperformed. Thereafter, a process of separating the LED structure inFIGS. 9 to 11 (FIG. 9K et seq, and FIG. 10D et seq.) or a process ofseparating the LED structure in FIG. 11 (FIG. 11D et seq.) may beperformed to separate an ultra-thin LED element 103 from the LED wafer.

Ultra-thin LED elements 101, 102, and 103 obtained through theabove-described methods may be implemented into an ink composition. Theink composition may further include a dispersion medium and otheradditives provided in a known inkjet ink composition, and the presentinvention is not particularly limited in that respect. However, asdescribed above, since a thickness and a length of a major axis in across section perpendicular to a stacking direction satisfy theabove-described specific ratio, when the ultra-thin LED elements 101,102, and 103 are made into an ink, precipitation is delayed, and thusthe ultra-thin LED elements 101, 102, and 103 have an advantage of beingable to maintain a dispersed state for a long time. In addition, aconcentration of the ultra-thin LED elements 101, 102, and 103 dispersedin an ink composition and a viscosity of the ink composition can bedesigned to be suitable for an inkjet printing apparatus for performingprinting using the ink composition, and the present invention is notparticularly limited in that respect. In addition, the inkjet printingapparatus may be an apparatus capable of performing printing using anink composition including ultra-thin LED elements on a lower electrodeand an apparatus adopting a known method such as a piezoelectric methodor an electrostatic method. Thus, the present invention is notparticularly limited to an inkjet printing apparatus and a specificmethod of performing printing on a lower electrode using the same.

Next, as operation 2-2 according to the present invention, an operationof processing the ultra-thin LED elements 101, 102, and 103 on lowerelectrodes 311 and 312, for example, erecting and assembling theultra-thin LED elements 101, 102, and 103 in a thickness directionthereof on the lower electrodes 311 and 312 through an inkjet printingapparatus, is performed.

After a plurality of ultra-thin LED elements 101, 102, and 103 dispersedin the ink composition are printed on the lower electrodes, all of theultra-thin LED elements may be positioned in an arrangement region onthe lower electrodes in which the ultra-thin LED elements are to bedisposed. In addition, even if the ultra-thin LED elements 101, 102, and103 are positioned within the arrangement region, all the ultra-thin LEDelements may not be erected and disposed on the lower electrodes in thethickness direction.

Thus, as described above, in an ultra-thin LED electrode assembly 1000,an arrangement guide layer 70 for erecting and arranging the ultra-thinLED elements 101, 102, and 103 in the thickness direction may be furtherincluded at one side of the ultra-thin LED element 101, 102, and 103 inthe thickness and one side or both sides of the arrangement region inwhich the ultra-thin LED elements 101, 102, and 103 are to be disposed.

Specifically, referring to FIG. 13 , when the arrangement guide layer 70is a charge layer 71 having positive or negative charges, after printingis performed using an ink composition including ultra-thin LED elements,together with or before printing, ultra-thin LED elements 104 may bemoved to an arrangement region through an electrophoresis method, and anelectric field may be formed in a direction perpendicular to a mainsurface of a lower electrode 311 such that the ultra-thin LED elements104 are erected and disposed in a thickness direction thereof. Inaddition, when the charge layer, which is provided in the ultra-thin LEDelement such that the ultra-thin LED element is advantageously moved anderected in the arrangement region, is a first charge layer havingpositive or negative charges, a second charge layer that has chargesopposite to those of the first charge layer may be provided in thearrangement region on the lower electrode. The first charge layer andthe second charge layer may have a thickness of, for example, 0.1 nm to500 nm, but since the first charge layer and the second charge layer areformed only to have a thickness sufficient to have charges, the presentinvention is not particularly limited in that respect.

In addition, since an intensity of an electric field for moving anderecting the ultra-thin LED element in the arrangement region through anelectrophoresis method can also be appropriately changed inconsideration of the number and size of the ultra-thin LED elements inthe ink composition, the present invention is not particularly limitedin that respect.

Alternatively, to describe a case in which the arrangement guide layer70 is a bonding layer 72 with reference to FIG. 14 , by using a chemicalbond through the bonding layer 72, ultra-thin LED elements 105 may beerected and assembled in an arrangement region. In this case, thebonding layer 72 may be provided at one side of the ultra-thin LEDelement 105 in a thickness direction thereof and/or in the arrangementregion.

In addition, the bonding layer may be formed such that, for example, athiol group, an amine group, a carboxyl group, a DNA single strand, orthe like is exposed to the outside. Specifically, the bonding layer maybe made of a compound such as aminoethanethiol, 1,2-ethanedithiol,1,4-butanedithiol, 3-mercaptopropionic acid, or a NH₂-terminated DNAsingle strand. In addition, the chemical bond may be a covalent bond ora non-covalent bond, and as an example, a bonding layer in which a thiolgroup is exposed to the outside may be bonded to a lower electrode madeof a metal through a non-covalent bond. In addition, since a reactionrate is very slow when an amine group and a carboxyl group combine toform an amide bond, after 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC) is added to form an active ester intermediate with a carboxylgroup, a strong nucleophilic primary amine may be added to rapidly forman amide bond. In addition, in order to stabilize an ester intermediateusing EDC, sulfo-N-hydroxysuccinimide (NHS) may be used so that an amidebond can proceed stably. In addition, the chemical bond may be acovalent bond or a non-covalent bond, and as an example, a bonding layerin which a thiol group is exposed to the outside may be bonded to alower electrode made of a metal through a non-covalent bond. Inaddition, the bonding layer may include a first bonding layer formed ata side of the ultra-thin LED element and a second bonding layer formedat a side of the lower electrode side, and through a complementary bondbetween a first linker in the first bonding layer and a second linker inthe second bonding layer, the ultra-thin LED element may be erected andassembled on the lower electrode.

Alternatively, to describe a case in which the arrangement guide layer70 is a magnetic layer 73 with reference to FIG. 15 , in order forultra-thin LED elements 106 to move to an arrangement region through amagnetic force to be erected and disposed in a thickness directionthereof, after printing is performed using an ink composition includingthe ultra-thin LED elements, together with or before printing, amagnetic field may be formed in a direction perpendicular to a mainsurface of a lower electrode 311. In addition, a magnetic layer may alsobe formed in the arrangement region on the lower electrode such that theultra-thin LED element 106 is advantageously moved and erected in thearrangement region. The magnetic layer may be made of a paramagneticmaterial or a ferromagnetic material. In addition, the magnetic layer 73may have a thickness of, for example, 0.1 nm to 500 nm, but the presentinvention is not particularly limited thereto.

Thereafter, an operation of fixing the ultra-thin LED elements 104, 105,and 106, which are erected and disposed on the lower electrodes 311 and312, and bringing the ultra-thin LED elements 104, 105, and 106 intoohmic contact with the lower electrodes 311 and 312 may be furtherperformed. The fixing and ohmic contact may be performed, for example,through an RTA process on an interface between the lower electrode andthe ultra-thin LED element. Alternatively, a fixing layer having a lowmelting point is further provided in the arrangement region on the lowerelectrodes 311 and 312, the ultra-thin LED elements 104, 105, and 106may be erected and disposed in the arrangement region, and then heat maybe applied to melt and solidify the fixing layer, thereby firmly fixingthe ultra-thin LED elements 104, 105, and 106 onto the lower electrodes311 and 312. The fixing layer may be made of, for example, a typicalsolder material used as an electrical/electronic material.

Meanwhile, in order to improve electrical connectivity between theultra-thin LED elements 104, 105, and 106 and the lower electrodes 311and 312, after operation 2-2, an operation of forming a conducting metallayer 500 may be further performed. A line on which a conducting metallayer is to be deposited may be patterned by applying a photolithographyprocess using a photosensitive material to then deposit the conductingmetal layer, or a deposited metal layer may be patterned and thenetched, thereby manufacturing the conducting metal layer 500. Such aprocess may be performed by appropriately adopting a known method, and10-2016-0181410 by the inventor of the present invention may beincorporated by reference.

In addition, between processes of operations 2 and 3, an operation offorming an insulating layer 600 having a certain thickness on a lowerelectrode line 310 for electrical insulation from an upper electrodeline 320 may be further performed. The insulating layer 600 may beformed by depositing a known insulating material. As an example, aninsulating material such as SiO₂ or SiN, may be deposited through aplasma enhanced chemical vapor deposition (PECVD) method, an insulatingmaterial such as AlN or GaN may be deposited through a metal-organicchemical vapor deposition (MOCVD) method, or an insulating material suchas Al₂O, HfO₂, or ZrO₂ may be deposited through an atomic layerdeposition (ALD) method. Meanwhile, it is preferable that the insulatinglayer 600 be formed not to cover upper surfaces of the ultra-thin LEDelements 104, 105, and 106 which are erected and assembled. To this end,an insulating layer may be formed through deposition to a thickness notto cover the upper surfaces of the ultra-thin LED elements 104, 105, and106, or after an insulating layer is deposited to a thickness so as tocover the upper surfaces of the ultra-thin LED elements 104, 105, and106, dry etching may be performed before the upper surfaces of theultra-thin LED elements 104, 105, and 106 are exposed.

Next, as operation 3 according to the present invention, an operation offorming the upper electrode line 320 including upper electrodes 321 and322 to be electrically connected to an opposite side opposite to oneside of the ultra-thin LED elements 104, 105, and 106 electricallyconnected to the lower electrodes 311 and 312 is performed. An electrodeline may be patterned using known photolithography to then deposit anelectrode material, or an electrode material may be deposited and thenbe dry- and/or wet-etched, thereby implementing the upper electrode line320. In this case, the electrode material may be a typical electrodematerial used as an electrode of an electrical/electronic material, andthe present invention is not particularly limited in that respect.

Next, an exemplary embodiment of a micro-nanofin ultra-thin LEDelectrode element and an LED electrode assembly using the same will bedescribed.

[Second (Micro-Nanofin) Type Ultra-Thin LED Electrode Element and LEDElectrode Assembly]

An LED electrode assembly manufactured using second type ultra-thin LEDelements will now be described with reference to FIGS. 16 and 17 . Ablank portion in FIG. 16 indicates one pixel unit in the LED electrodeassembly, and the pixel unit is illustrated in a schematic view asincluding three subpixel units (first to third subpixel units) whicheach include six micro-nanofin LED elements.

A micro-nanofin LED electrode assembly 100 l according to an exemplaryembodiment of the present invention includes a lower electrode line 200including a plurality of electrodes 211, 212, 213, and 214 spaced acertain interval from each other in a horizontal direction, a pluralityof micro-nanofin LED elements 107 disposed on the lower electrode line200, and an upper electrode line 300 disposed in contact with upperportions of the micro-nanofin LED elements 107.

First, prior to a detailed description of each component, electrodelines for allowing the micro-nanofin LED elements to be self-aligned andemit light will be described.

The micro-nanofin LED electrode assembly 100 l includes the upperelectrode line 300 and the lower electrode line 200 disposed at an upperside and a lower side to face each other with the micro-nanofin LEDelements 107 interposed therebetween. Since the upper electrode line 300and the lower electrode line 200 are not arranged in the horizontaldirection, an electrode design may be highly simplified and more easilyimplemented by breaking away from a complicated electrode line of aconventional electrode assembly using electric field induction, in whichtwo types of electrodes implemented to have an ultra-thin thickness andwidth are arranged at micro or nano unit intervals within a planarsurface with a limited area in the horizontal direction.

In detail, even in a conventional electrode assembly implemented byself-aligning elements through electric field induction, by usingelectrodes spaced from each other in the horizontal direction asassembly electrodes, rod-type ultra-small LED elements are mounted onthe assembly electrodes, and the same electrode, that is, the assemblyelectrode, is used as a driving electrode without any change. However,since the lower electrode line 200 provided in an exemplary embodimentof the present invention functions as an assembly electrode, but only asurface at a side of a first conductive semiconductor layer or a surfaceat a side of a second conductive semiconductor layer is in contact withthe lower electrode line 200, the micro-nanofin LED electrode assembly100 l is different from the conventional electrode assembly throughelectric field induction in that the micro-nanofin LED element 107cannot emit light only with the lower electrode line 200. Such adifference causes significant differences in degree of freedom of anelectrode design and in easiness of the electrode design.

That is, when an assembly electrode and a driving electrode are used asthe same electrode, since it is necessary to implement a structure inwhich rod-type ultra-small LED elements can be mounted in as manynumbers as possible on a planar surface having a limited area andsimultaneously to implement electrodes, to which different voltages areapplied, at intervals of a micro/nano size, it has not been easy todesign or implement an electrode structure.

However, since the same type of power (for example, positive or negativepower) is applied to the lower electrode line 200 included in thepresent invention during driving, there is little risk of an electricshort circuit between the lower electrodes 211, 212, 213, and 214 in thelower electrode line 200.

In addition, conventionally, both end portions of each rod-typeultra-small LED element had to be in contact with adjacent electrodes inone-to-one correspondence for light to be emitted without an electricalshort circuit. Therefore, when an individual rod-type ultra-small LEDelement is disposed over three or four adjacent electrodes, aphotoactive layer of the rod-type ultra-small LED element is inevitablyin contact with the electrode, and thus a short circuit occurs,resulting in difficulty in designing the electrode in consideration ofpreventing the short circuit. However, in the micro-nanofin LED element107 included in the present invention, since the surface at the side ofthe first conductive semiconductor layer or the surface at the side ofthe second conductive semiconductor layer is in contact with the lowerelectrode line, and thus an electrical short circuit does not occur evenwhen the micro-nanofin LED element 107 is disposed over the plurality ofadjacent lower electrodes 211, 212, 213, and 214, which has an advantagein that the lower electrode line 200 can be more easily designed.

In addition, since the upper electrode line 300 is disposed only to bein electrical contact with an upper surface of the micro-nanofin LEDelement 107 as shown in FIG. 16 , there is an advantage in that anelectrode is very easily designed or implemented. In particular,although FIG. 16 illustrates that the upper electrode line 300 isimplemented to be divided into a first upper electrode 301 and a secondupper electrode 302, only one electrode can also be implemented to be incontact with the upper surfaces of all the disposed micro-nanofin LEDelements, and thus there is an advantage in that an electrode can beimplemented to be highly simplified as compared with a related art.

The lower electrode line 200 serves as one of an assembly electrode forself-aligning the micro-nanofin LED element 107 such that the uppersurface or a lower surface of the micro-nanofin LED element 107 in athickness direction thereof is in contact therewith and a drivingelectrode provided to allow, together with the upper electrode line 300which will be described below, the micro-nanofin LED element 107 to emitlight.

In addition, the lower electrode line 200 is implemented to include theplurality of lower electrodes 211, 212, 213, and 214 spaced a certaininterval from each other in the horizontal direction. The number andinterval of the lower electrodes 211, 212, 213, and 214 may be thenumber and interval of the electrodes 211, 212, 213, and 214 which areappropriately set in consideration of a function as an assemblyelectrode, a length of an element, and the like.

In addition, as long as the plurality of lower electrodes 211, 212, 213,and 214 included in the lower electrode line 200 are disposed apart fromeach other in the horizontal direction, there is no limitation on aspecific electrode arrangement. As an example, the lower electrode line200 may have a structure in which a plurality of electrodes are spaced acertain interval from each other in one direction and disposed inparallel.

Meanwhile, an interval between the adjacent electrodes 211 and 212 maybe shorter than a length of a micro-nanofin LED element 100 or 107, whenthe interval between two adjacent electrodes is longer than or equal tothe length of the micro-nanofin LED element, the micro-nanofin LEDelement may be self-aligned in a form in which it is sandwiched betweenthe two adjacent electrodes. This is not preferable because there is ahigh risk of an electrical short circuit occurring due to contactbetween a side surface of the electrode and the photoactive layerexposed at a side surface of the micro-nanofin LED element.

In addition, when the upper electrode line 300 is designed to be inelectrical contact with the upper portion of the micro-nanofin LEDelement 107 mounted on the lower electrode line 200, there is nolimitation on the number, arrangement, or the like thereof. However,when the lower electrode lines 200 are arranged in parallel in onedirection as shown in FIG. 16 , the upper electrode line 300 may bearranged to be perpendicular to the one direction, and such an electrodearrangement is an electrode arrangement widely used in a conventionaldisplay field and has an advantage in that an electrode arrangement andcontrol technology of the conventional display field can be used withoutany change.

Meanwhile, although FIG. 16 illustrates only the first upper electrode301 and the second upper electrode 302 so that the upper electrode line300 including the first upper electrode 301 and the second upperelectrode 302 covers only some elements, other upper electrodes areomitted for ease of description, and there are further unillustratedupper electrodes disposed on the micro-nanofin LED element.

Since the lower electrode line 200 and the upper electrode line 300 mayhave a material, shape, width, and thickness of an electrode used in atypical LED electrode assembly and may be manufactured using a knownmethod, the present invention is not specifically limited in thatrespect. As an example, the electrodes may be made of aluminum,chromium, gold, silver, copper, graphene, ITO, or an alloy thereof andmay have a width of 0.1 μm to 50 μm and a thickness of 0.1 μm to 100 μmbut may be appropriately changed in consideration of the size or thelike of a desired LED electrode assembly.

Next, the micro-nanofin LED element 107 disposed between the lowerelectrode line 200 and the upper electrode line 300 described above willbe described.

Referring to FIGS. 17 to 19 , when it is assumed that, with respect toX, Y, and Z axes that are perpendicular to each other, an X-axisdirection indicates a length, a Y-axis direction indicates a width, anda Z-axis direction indicates a thickness, the micro-nanofin LED element107 according to an exemplary embodiment of the present invention is arod-type element in which a length corresponds to a long axis, athickness corresponds to a short axis, and the length is greater thanthe thickness and is an element in which a first conductivesemiconductor layer 10, a photoactive layer 20, a second conductivesemiconductor layer 30, and a polarization inducing layer 90 aresequentially stacked in a thickness direction thereof.

More specifically, the micro-nanofin LED element 107 has a certain shapein an X-Y plane having a length and a width, a direction perpendicularto the plane is the thickness direction, and each layer is stacked inthe thickness direction. Even when the photoactive layer 20 at a portionexposed at a side surface of the micro-nanofin LED element is thin, themicro-nanofin LED element has an advantage in that a wider lightemitting area can be secured due to a planar surface having a length anda width. In addition, the micro-nanofin LED element 100 according to anexemplary embodiment of the present invention may thus have a wide lightemitting area exceeding twice an area of a longitudinal cross section ofthe micro-nanofin LED element. Here, the longitudinal cross section is across section parallel to the X-axis direction that is a lengthdirection, and in the case of an element having a constant width, thelongitudinal cross section may correspond to the X-Y plane.

Specifically, referring to FIGS. 20A and 20B, both of a first rod-typeelement 1 shown in FIG. 20A and a second rod-type element 1′ shown inFIG. 20B are rod-type elements which have a structure in which a firstconductive semiconductor layer 10, a photoactive layer 20, and a secondconductive semiconductor layer 30 are stacked, which have the samelength t and the same thickness m, and of which the photoactive layersalso have the same thickness h. However, there is a structuraldifference in that, in the first rod-type element 1, the firstconductive semiconductor layer 10, the photoactive layer 20, and thesecond conductive semiconductor layer 30 are stacked in a thicknessdirection thereof, and in the second rod-type element 1′, the firstconductive semiconductor layer 10, the photoactive layer 20, and thesecond conductive semiconductor layer 30 are stacked in a lengthdirection thereof.

However, the two elements 1 and 1′ have a significant difference inlight emitting area. As an example, when it is assumed that the length lis 4,500 nm, the thickness m is 600 nm, and the thickness h of thephotoactive layer 20 is 100 nm, a ratio of a surface area of thephotoactive layer 20 of the first rod-type element 1 and a surface areaof the photoactive layer 20 of the second rod-type element 1′ is 6.42μm²:0.75 μm², and thus a light emitting area of the first rod-type LEDelement 1 is about 8.56 times greater, wherein the surface areacorresponds to the light emitting area. In addition, the first rod-typeelement 1 is similar to the second rod-shaped element 1′ in a ratio of asurface area of the photoactive layer 20 exposed to the outside to atotal light emitting area of the photoactive layer. However, since theabsolute value of an increased unexposed surface area of the photoactivelayer 20 is increased much to greatly reduce an influence of the exposedsurface area on excitons, an influence of surface defects of the firstrod-type LED element 1 on excitons is greatly decreased as compared withthe horizontally arranged rod-type element 1′. Thus, it can be evaluatedthat the first rod-type LED element 1 is considerably superior to thehorizontally arranged rod-type element 1′ in terms of luminousefficiency and brightness. Also, the second rod-type element 1′ isimplemented by etching a wafer in which a conductive semiconductor layerand a photoactive layer are stacked in a thickness direction thereof.After all, a long element length corresponds to a wafer thickness, andin order to increase the element length, an increase in etch depth isinevitable. As the etch depth is increased, a possibility of occurrenceof surface defects of an element increases. As a result, the secondrod-type element 1′ has a higher possibility of occurrence of surfacedefects even though an area of the exposed photoactive layer is smallerthan that of the first rod-typed element 1. Therefore, considering adecrease in luminous efficiency due to an increase in possibility ofoccurrence of surface defects, the first rod-type element 1 may beconsiderably superior in luminous efficiency and brightness.

Furthermore, a movement distance of holes injected from any one of thefirst conductive semiconductor layer 10 and the second conductivesemiconductor layer 30 and electrons injected from the other in thefirst rod-type element 1 is shorter than that of the second rod-typeelement 1′, and thus a probability of electrons and/or holes beingcaptured by defects on a wall during movement of electrons and/or holesis low. Therefore, an emission loss can be minimized, and it can also beadvantageous in minimizing an emission loss due to an electron-holevelocity imbalance. In addition, in the case of the second rod-typeelement 1′, since a strong optical path behavior occurs due to acircular rod-type structure, a path of light generated by electron-holepairs resonates in a length direction thereof, and thus light is emittedfrom both end portions thereof in the length direction. Therefore, whenthe element is disposed to lie down, front luminous efficiency is notgood due to a strong side emission profile. On the other hand, in thecase of the first rod-type element 1, since light is emitted from anupper surface and a lower surface thereof, there is an advantage in thatexcellent front luminous efficiency is exhibited.

In the micro-nanofin LED element 107 of the present invention, like thefirst rod-type element 1 described above, the conductive semiconductorlayers 10 and 30 and the photoactive layer 20 are stacked in thethickness direction, and the length is implemented to be longer than thethickness, thereby further increasing a light emitting area. At the sametime, since the micro-nanofin LED element 107 is a rod type in which,even when an area of the exposed photoactive layer 20 is slightlyincreased, a thickness is shorter than a length, an etched depth isshallow, and thus a possibility of occurrence of defects on an exposedsurface of the photoactive layer 20 can be reduced, which isadvantageous in minimizing or preventing a decrease in luminousefficiency due to defects.

Although a planar surface is illustrated in FIG. 17 as having arectangular shape, the present invention is not limited thereto, and ageneral quadrangular shape, such as a rhombic shape, a parallelogramshape, or a trapezoidal shape as well as an oval shape may be adoptedwithout limitation.

The micro-nanofin LED element 107 according to an exemplary embodimentof the present invention may have a length and a width of a micro ornano unit. As an example, the element may have a length of 100 nm to6,000 nm and a width of 100 nm to 3,000 nm. In addition, the element mayhave a thickness of 100 nm to 2,000 nm. Standards of the length andwidth may differ according to a shape of a planar surface. As anexample, when the planar surface has a rhombic shape or a parallelogramshape, one of two diagonals may be a length, and the other may be awidth, and when the planar surface has a trapezoidal shape, the longestof a height, an upper side, and a lower side may be a length, and theshortest one perpendicular to the longest one may be a width.Alternatively, when the planar surface has an oval shape, a major axisof the oval shape may be a length, and a minor axis thereof may be awidth.

In this case, a ratio of a thickness and a length of the micro-nanofinLED element 100 may be 1:3 or more and more preferably 1:6 or more sothat the length may be longer. Therefore, there is an advantage in thatthe micro-nanofin LED element 100 can be more easily self-aligned on thelower electrode through an electric field. When the ratio of thethickness and the length of the micro-nanofin LED element 100 is lessthan 1:3 so that the length is decreased, it may be difficult toself-align the element on the electrode through an electric field, andsince the element is not fixed onto the lower electrode, there may be arisk of an electrical contact short circuit caused by a process defect.However, the ratio of the thickness and the length may be 1:15 or less,and thus it may be advantageous in achieving the object of the presentinvention, such as optimization of torque by which the micro-nanofin LEDelement 100 is self-aligned through an electric field.

In addition, a ratio of a width and a length in the planar surface mayalso be preferably 1:3 or more and more preferably 1:6 or more so thatthe length may be longer. Accordingly, there is an advantage in that themicro-nanofin LED element can be more easily self-aligned on the lowerelectrode through an electric field. However, the ratio of the width andthe length may be 1:15 or less, and thus it may be advantageous inoptimizing torque by which the micro-nanofin LED element is self-alignedthrough an electric field.

In addition, a width of the micro-nanofin LED element 107 may be greaterthan or equal to the thickness, and thus when the micro-nanofin LEDelement is aligned on the lower electrode line using an electric field,there is an advantage in that the micro-nanofin LED element can beminimized or prevented from lying on its side when aligned. When themicro-nanofin LED element is aligned lying on its side, even ifalignment and mounting, in which one end portion and the other endportion are in contact with two adjacent lower electrodes 211/212 or213/214, are achieved, there is a risk that the element may not emitlight due to an electrical short circuit that occurs when an exposedside surface of the photoactive laver in the element comes into contactwith an electrode.

In addition, the micro-nanofin LED element 107 may be an element ofwhich both end portions in a length direction thereof have differentsizes. As an example, the micro-nanofin LED element 107 may be arod-type element having a quadrangular planar surface that has anequilateral trapezoidal shape of which a height, that is, a length, islonger than upper and lower sides. As a result, due to a difference inlength between the upper side and the lower side, a difference betweenpositive charges and negative charges accumulated at both end portionsof the element in a length direction thereof may occur. Therefore, thereis an advantage in that self-alignment can be easier through an electricfield.

In addition, a protrusion 11 having a certain width and thickness may beformed on a lower surface of the first conductive semiconductor layer 10of the micro-nanofin LED element 107 in the length direction of theelement, or a protrusion may not be formed.

The protrusion 11 will be described in detail in description of amanufacturing method described below. The protrusion 11 may be formed byetching a wafer in a thickness direction thereof and then horizontallyperforming etching from both side surfaces of a lower end portion of anetched LED part toward an inner side, that is, a central portion, toseparate the etched LED part from the wafer. The protrusion 11 mayassist in performing a function of improving extraction of top emissionof the micro-nanofin LED element. In addition, when the micro-nanofinLED element is self-aligned on the lower electrode line, the protrusion11 may assist in controlling alignment such that the polarizationinducing layer 90, which is opposite to one surface of the element onwhich the protrusion 11 is formed, is positioned on the lower electrodeline 200. Furthermore, the polarization inducing layer is positioned onthe lower electrode line 200, and the upper electrode line 300 is formedon one surface of the element on which the protrusion 11 is formed. Theprotrusion 11 may increase a contact area with the upper electrode line300 to be formed, and thus it may be advantageous in improving amechanical coupling force between the upper electrode line 300 and themicro-nanofin LED element 100.

In this case, a width of the protrusion 11 may be formed to be less thanor equal to 50% of the width of the micro-nanofin LED element and morepreferably less than or equal to 30% thereof, and thus the micro-nanofinLED element etched on an LED wafer may be easily separated. When theprotrusion is formed such that the width exceeds 50% of the width of themicro-nanofin LED element, it may not be easy to separate a part of themicro-nanofin LED element etched on the LED wafer, and parts other thana desired part may be separated. Thus, productivity may be reduced, andthere may be a risk that the uniformity of a plurality of manufacturedmicro-nanofin LED elements may be reduced. Meanwhile, the width of theprotrusion 11 may be formed to be 10% or more of the width of themicro-nanofin LED element. When the width of the protrusion is formed tobe less than 10% of the width of the micro-nanofin LED element, themicro-nanofin LED element may be easily separated from the LED wafer,but during lateral etching (see FIGS. 21G and 21I) which will bedescribed below, there may be a risk that even a portion of the firstconductive semiconductor layer that should not be etched may be etcheddue to excessive etching, and the above-described effect through theprotrusion 11 may not be exhibited. In addition, there may be a riskthat the element may be damaged by a wet etching solution, and there maybe a problem that the micro-nanofin LED element dispersed in a high-risketching solution having a strong basic property needs to be cleaned bybeing separated from the wet etching solution. Meanwhile, a thickness ofthe protrusion 11 may be in a range of 10% to 30% of a thickness of thefirst conductive semiconductor layer. Thus, the first conductivesemiconductor layer may be formed to have a desired thickness andquality, and it may be more advantageous in exhibiting an effect throughthe above-described protrusion 11. Here, the thickness of the firstconductive semiconductor layer is a thickness based on a lower surfaceof the first conductive semiconductor layer on which the protrusion isnot formed.

As a specific example, the protrusion 11 may have a width of 50 nm to300 nm and a thickness of 50 nm to 900 nm.

Hereinafter, each layer included in the micro-nanofin LED element 107will be described.

The micro-nanofin LED element includes the first conductivesemiconductor layer 10 and the second conductive semiconductor layer 30.A conductive semiconductor layer adopted in a typical LED element usedfor lighting, display, and the like may be used as the used conductivesemiconductor layer without limitation. According to an exemplaryembodiment of the present invention, any one of the first conductivesemiconductor layer 10 and the second conductive semiconductor layer 30may include at least one n-type semiconductor layer, and the other mayinclude at least one p-type semiconductor layer.

When the first conductive semiconductor layer 10 includes the n-typesemiconductor layer, the n-type semiconductor layer may include asemiconductor material having an empirical formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, atleast one selected from among InAlGaN, GaN, AlGaN, InGaN, AlN, and InN.The n-type semiconductor layer may be doped with a first conductivedopant (for example, Si, germanium (Ge), or tin (Sn)). According to anexemplary embodiment of the present invention, the first conductivesemiconductor layer 10 may have a thickness of 1.5 μm to 5 μm, but thepresent invention is not limited thereto. The thickness of the firstconductive semiconductor layer 10 is preferably greater than or equal tothat of the second conductive semiconductor layer 30.

When the second conductive semiconductor layer 30 includes the p-typesemiconductor layer, the p-type semiconductor layer may include asemiconductor material having an empirical formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, atleast one selected from among InAlGaN, GaN, AlGaN, InGaN, AlN, and InN.The p-type semiconductor layer may be doped with a second conductivedopant (for example, Mg). According to an exemplary embodiment of thepresent invention, the second conductive semiconductor layer 30 may havea thickness of 0.01 μm to 0.30 μm, but the present invention is notlimited thereto. The thickness of the second conductive semiconductorlayer 30 is preferably less than or equal to that of the firstconductive semiconductor layer 10.

According to an exemplary embodiment of the present invention, any oneof the first conductive semiconductor layer 10 and the second conductivesemiconductor layer 30 includes a p-type GaN semiconductor layer, andthe other includes an n-type GaN semiconductor layer. The p-type GaNsemiconductor layer may have a thickness of 10 nm to 350 nm, and then-type GaN semiconductor layer may have a thickness of 100 nm to 3,000nm. Thus, a movement distance of holes injected into the p-type GaNsemiconductor layer and electrons injected into the n-type GaNsemiconductor layer is shorter as compared with the rod-type element inwhich the semiconductor layer and the photoactive layer are stacked inthe length direction as shown in FIG. 21B. As a result, a probability ofelectrons and/or holes being captured by defects on a wall duringmovement is low so that an emission loss can be minimized, and it canalso be advantageous in minimizing an emission loss due to anelectron-hole velocity imbalance.

Next, the photoactive layer 20 may be formed on the first conductivesemiconductor layer 10 and may be formed in a single or multi-quantumwell structure. A photoactive layer included in a typical LED elementused for lighting, display, and the like may be used as the photoactivelayer 20 without limitation. A clad layer (not shown) doped with aconductive dopant may be formed on and/or under the photoactive layer 20and may be implemented as an AlGaN layer or an InAlGaN layer. Inaddition, a material such as AlGaN or AlInGaN may be used for thephotoactive layer 20. Regarding the photoactive layer, when an electricfield is applied to the element, electrons and holes move from theconductive semiconductor layers positioned above and under thephotoactive layer to the photoactive layer, and electron-hole pairs aregenerated in the photoactive layer, thereby emitting light. According toan exemplary embodiment of the present invention, the photoactive layer20 may have a thickness of 30 nm to 300 nm, but the present invention isnot limited thereto.

Next, since the polarization inducing layer 90 formed on the secondconductive semiconductor layer 30 described above has both end portionshaving different electrical polarities in the length direction of theelement, the polarization inducing layer 90 may serve as a layer whichfacilitates self-alignment though an electric field, and at the sametime, when a material such as a metal is used, the polarization inducinglayer 90 may increase conductivity to serve as an electrode layer.

In addition, a first polarization inducing layer 91 may be disposed onone end side of the polarization inducing layer 90 in a length directionof the element, and a second polarization inducing layer 92 may bedisposed at the other end side thereof. The first polarization inducinglayer 91 and the second polarization inducing layer 92 may havedifferent electrical polarities. As an example, the first polarizationinducing layer 91 may be made of ITO, and the second polarizationinducing layer 92 may be made of a metal, a dielectric, or asemiconductor. In addition, the polarization inducing layer 90 may havea thickness of 50 nm to 500 nm, but the present invention is not limitedthereto. An upper surface of the second conductive semiconductor layer30 may be bisected to arrange the first polarization inducing layer 91and the second polarization inducing layer 92 to have the same area, butthe present invention is not limited thereto. Any one of the firstpolarization inducing layer 91 and the second polarization inducinglayer 92 may be disposed to have a larger area.

The first conductive semiconductor layer 10, the photoactive layer 20,the second conductive semiconductor layer 30, and the polarizationinducing layer 90 may be included as minimal components of the LEDelement, and another phosphor layer, an active layer, a semiconductorlayer, a hole block layer, and/or an electrode layer may be furtherincluded on/under each layer.

Meanwhile, according to an exemplary embodiment of the presentinvention, a protective film 80 formed on the side surface of themicro-nanofin LED element to cover the exposed surface of thephotoactive layer 20 may be further included. The protective film 80 isa film for protecting the exposed surface of the photoactive layer 20,and may cover the entirety of the exposed surface of the photoactivelayer 20, for example, at least all of both side surfaces and front andrear surfaces of the micro-nanofin LED element. The protective film 80may preferably include at least one selected from among silicon nitride(Si₃N₄), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), hafnium oxide(HfO₂), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃), titanium dioxide(TiO₂), aluminum nitride (AlN), and gallium nitride (GaN) and may bemore preferably made of the above component materials and may betransparent, but the present invention is not limited thereto. Accordingto an exemplary embodiment of the present invention, the protectivelayer 80 may have a thickness of 5 nm to 200 nm, but the presentinvention is not limited thereto.

The micro-nanofin LED element 107 may be manufactured through amanufacturing method which will be described below, but the presentinvention is not limited thereto. Specifically, a micro-nanofin LEDelement may be manufactured by performing operation A of providing anLED wafer in which a first conductive semiconductor layer, a photoactivelayer, and a second conductive semiconductor layer are sequentiallystacked on a substrate, operation B of forming a polarization inducinglayer patterned on the second conductive semiconductor layer of the LEDwafer such that regions having different electrical polarities areadjacent to each other, operation C of etching the LED wafer in athickness direction thereof such that an individual element has a planarsurface with a length and width of a nano or micro size, and a thicknessperpendicular to the planar surface is shorter than the length andforming a plurality of micro-nanofin LED pillars, and operation D ofseparating the plurality of micro-nanofin LED pillars from thesubstrate.

Referring to FIG. 21 , first, as operation A of the present invention,an operation of providing an LED wafer 51 in which a first conductivesemiconductor layer 10, a photoactive layer 20, and a second conductivesemiconductor layer 30 are sequentially stacked on the substrate (notshown) is performed.

Since description of each layer provided in the LED wafer 51 is the sameas the above description, detailed description thereof will be omitted,and parts which have not been described will be mainly described.

First, the first conductive semiconductor layer 10 in the LED wafer 51may be thicker than the first conductive semiconductor layer 10 in themicro-nanofin LED element 100 described above. In addition, each layerin the LED wafer 51 may have a c-plane crystal structure.

The LED wafer 51 may have been subjected to a cleaning process, andsince a typical wafer cleaning solution and cleaning process may beappropriately adopted for the cleaning process, the present invention isnot particularly limited in that respect. The cleaning solution may be,for example, isopropyl alcohol, acetone, or hydrochloric acid but is notlimited thereto.

Next, as operation B of the present invention, as shown in FIGS. 21B and21C1/21C2, an operation of forming a polarization inducing layer 90 onthe second conductive semiconductor layer 30 of the LED wafer 51 isperformed. Specifically, the polarization inducing layer 90 may bepatterned on the second conductive semiconductor layer of the LED wafersuch that regions having different electrical polarities are adjacent toeach other. More specifically, operation B may include operation B-1 offorming a first polarization inducing layer 91 on the second conductivesemiconductor layer 30 as shown in FIG. 21B, operation B-2 of etchingthe first polarization inducing layer 91 along a certain pattern in athickness direction thereof, and operation B-3 of forming a secondpolarization inducing layer 92 on an etched intaglio portion as shown inFIGS. 21C1 and 21C2.

First, as operation B-1, an operation of forming the first polarizationinducing layer 91 on the second conductive semiconductor layer 30 isperformed. The first polarization inducing layer 91 may be a typicalelectrode layer formed on a semiconductor layer, may be made of, forexample, Cr, Ti, Ni, Au, ITO, or the like and may be preferably made ofITO in terms of transparency. The first polarization inducing layer 91may be formed through a typical method of forming an electrode on asemiconductor layer, for example, through a deposition process usingsputtering. As an example, when ITO is used, the first polarizationinducing layer 91 may be deposited to a thickness of 150 nm, may befurther subjected to an RTA process after the deposition process, andmay be processed, for example, at a temperature of 600° C. for 10minutes. However, since the RTA process may be appropriately adjusted inconsideration of the thickness, material, and the like of the firstpolarization inducing layer 91, the present invention is notparticularly limited thereto.

Next, as operation B-2, an operation of etching the first polarizationinducing layer 91 along the certain pattern in the thickness directionis performed. The operation may be an operation of providing a point atwhich the second polarization inducing layer 92, which will be describedbelow, is formed, and the pattern may be formed in consideration of anarea ratio and arrangement form of the first polarization inducing layer91 and the second polarization inducing layer 92 in an element. As anexample, as can be confirmed in FIG. 21D, the pattern may be formed suchthat the first polarization inducing layer 91 and the secondpolarization inducing layer 92 are alternately arranged in parallel.Since the pattern can be formed by appropriately applying a typicalphotolithography method or nanoimprinting method, detailed descriptionthereof will be omitted in the present invention.

The etching may be performed by adopting an appropriate known etchingmethod in consideration of a selected material of the first polarizationinducing layer 91. For example, when the first polarization inducinglayer 91 is made of ITO, the pattern may be etched through wet etching.In this case, an etched thickness may be etched down to an upper surfaceof the second conductive semiconductor layer 30, that is, the entiretyof ITO may be etched in the thickness direction, but the presentinvention is not limited thereto. Specifically, only a portion of ITOmay be etched in the thickness direction, and the second polarizationinducing layer 92 may be formed on the etched intaglio portion. In thiscase, an upper layer at one end portion of the element may be formed ina two-layer structure in which the first polarization inducing layer 91made of ITO and the second polarization inducing layer 92 are stacked.

Next, as operation B-3, an operation of forming the second polarizationinducing layer 92 on the etched intaglio portion may be performed. Amaterial that has different electrical polarity from that of theselected first polarization inducing layer 91 and is used in a typicalLED may be used for the second polarization inducing layer 92 withoutlimitation, and may be, for example, a metal, a dielectric, or asemiconductor, and specifically may be nickel or chromium. As a methodfor forming the first polarization inducing layer 91 and the secondpolarization inducing layer 92, a known method may be appropriatelyadopted according to a material, deposition, or the like, and thus thepresent invention is not particularly limited in that respect.

Next, as operation C of the present invention, an operation of etchingthe LED wafer 51 in the thickness direction such that the individualelement has the planar surface having a length and width of a nano ormicro size, and the thickness perpendicular to the planar surface isshorter than the length and forming a plurality of micro-nanofin LEDpillars 52.

Specifically, operation C may include operation C-1 of forming a maskpattern layer 61 on an upper surface of the polarization inducing layer90 such that the individual element has the planar surface having acertain shape with a length and width of a nano or micro size (see FIG.21D), operation C-2 of performing etching down to a partial thickness ofthe first conductive semiconductor layer 10 along the pattern in thethickness direction and forming the plurality of micro-nanofin LEDpillars 52 (see FIG. 21E), operation C-3 of forming an insulating film62 to cover exposed side surfaces of the micro-nanofin LED pillars 52(see FIG. 21F), operation C-4 of removing a portion of the insulatingfilm 62 formed on the first conductive semiconductor layer 10 such thatan upper surface A (see FIG. 21G) of the first conductive semiconductorlayer 10 between the adjacent micro-nanofin LED pillars 52 is exposed(see FIG. 21G), operation C-5 of further etching the first conductivesemiconductor layer 10 in the thickness direction through the exposedupper surface A (see FIG. 21G) of the first conductive semiconductorlayer and forming a portion B (see FIG. 21F) of the first conductivesemiconductor layer of which a side surface is exposed by as much as acertain thickness in a downward direction of the first conductivesemiconductor layer of the micro-nanofin LED pillar on which theinsulating film 62 is formed (FIG. 21H), operation C-6 of etching theportion B (see FIG. 21H) of the first conductive semiconductor layer, ofwhich the side surface is exposed, from both side surfaces thereoftoward a center thereof (see FIG. 21I), and operation C-7 of removingthe mask pattern layer 61 disposed on the polarization inducing layer 90and the insulating film 62 covering the side surface (see FIG. 21J).

First, as operation C-1, an operation of forming the mask pattern layer61 on the upper surface of the polarization inducing layer 90 such thatthe individual element has the planar surface having a certain shapewith a length and width of a nano or micro size (see FIG. 21D) isperformed.

The mask pattern layer 61 may be a layer that is patterned such that animplemented LED element has a desired planar shape and may be formedusing a known method and material used for etching an LED wafer. Themask pattern layer 61 may be, for example, a SiO₂ hardmask patternlayer. To briefly describe a method of forming the mask pattern layer61, the mask pattern layer 61 may be formed through an operation offorming an unpatterned SiO₂ hardmask layer on the polarization inducinglayer 90, an operation of forming a metal layer on the SiO₂ hardmasklayer, an operation of forming a certain pattern on the metal layer, anoperation of etching the metal layer and the SiO₂ hardmask layer alongthe pattern, and an operation of removing the metal layer.

The mask layer may be a layer using which the mask pattern layer 61 isformed and may be formed by, for example, depositing SiO₂. The masklayer may be formed to have a thickness of 0.5 μm to 3 μm, for example,1.2 μm. In addition, the metal layer may be, for example, an aluminumlayer, and the aluminum layer may be formed through deposition. Thecertain pattern formed on the formed metal layer may be for implementinga pattern of the mask pattern layer and may be a pattern formed througha typical method. As an example, the pattern may be formed throughphotolithography using a photosensitive material or may be a patternformed through a known nanoimprinting method, laser interferencelithography, electron beam lithography, or the like. Thereafter, anoperation of etching the metal layer and the SiO₂ hardmask layer alongthe formed pattern is performed. As an example, the metal layer may beetched using ICP, and the SiO₂ hardmask layer or an imprinted polymerlayer may be etched using a dry etching method such as an RIE method.

Next, an operation of removing the metal layer or other photosensitivematerial layers present on the etched SiO₂ hardmask layer or a polymerlayer remaining through an imprint method may be performed. The removingmay be performed through a typical wet etching or dry etching methodaccording to a material, and detailed description thereof will beomitted in the present invention.

FIG. 21D is a plan view of the SiO₂ hardmask pattern layer 61 on thepolarization inducing layer 90. After that, as operation C-2, anoperation of performing etching down to the partial thickness of thefirst conductive semiconductor layer 10 along the pattern in thethickness direction and forming the plurality of micro-nanofin LEDpillars 52 as shown in FIG. 21E may be performed. The etching may beperformed through a typical dry etching method such as an ICP method.

Next, as operation C-3, an operation of forming the insulating film 62to cover the exposed side surfaces of the micro-nanofin LED pillars 52as shown in FIG. 21F may be performed. The insulating film 62 applied onthe side surface may be formed through deposition, and a materialthereof may be, for example, SiO₂, but is not limited thereto. Theinsulating film 62 serves as a side mask layer, and specifically, in aprocess of etching the portion B of the first conductive semiconductorlayer in order to separate the micro-nanofin LED pillars 52 as shown inFIG. 21I, the insulating film 62 performs a function of leaving the sidesurface of the micro-nanofin LED pillar 52 and preventing damage due toan etching process. The insulating film 62 may have a thickness of 100nm to 600 nm, but the present invention is not limited thereto.

Next, as operation C-4, an operation of removing the portion of theinsulating film 62 formed on the first conductive semiconductor layer 10such that the upper surface A (see FIG. 21G) of the first conductivesemiconductor layer 10 between the adjacent micro-nanofin LED pillars 52is exposed as shown in FIG. 21G may be performed. The insulating film 62may be removed through an appropriate etching method in consideration ofa material, and as an example, the insulating film 62 made of SiO₂ maybe removed through dry etching such as RIE.

Then, as operation C-5, an operation of further etching the firstconductive semiconductor layer 10 in the thickness direction through theexposed upper surface A (see FIG. 21G) of the first conductivesemiconductor layer and forming the portion B (see FIG. 21H) of thefirst conductive semiconductor layer of which the side surface isexposed by the certain thickness in the downward direction of the firstconductive semiconductor layer of the micro-nanofin LED pillar on whichthe insulating film 62 is formed as shown in FIG. 21H may be performed.As described above, the exposed portion B of the first conductivesemiconductor layer 10 is a portion which is laterally etched in adirection parallel to a substrate (base substrate) in an operation whichw-ill be described below. A process of further etching the firstconductive semiconductor layer 10 in the thickness direction may beperformed through, for example, a dry etching method such as an ICPmethod.

Next, operation C-6 of laterally etching the portion B (see FIG. 21H) ofthe first conductive semiconductor layer, of which the side surface isexposed, in the direction parallel to the substrate as shown in FIG. 21Imay be performed. The lateral etching may be performed through wetetching. As an example, the wet etching may be performed at atemperature of 60° C. to 100° C. using a tetramethylammonium hydroxide(TMAH) solution.

Thereafter, after wet etching in a lateral direction is performed, asoperation C-7, an operation of removing the mask pattern layer 61disposed on the polarization inducing layer 90 and the insulating film62 covering the side surface as shown in FIG. 21J may be performed. Bothmaterials of the mask pattern layer 61 disposed on the polarizationinducing layer 90 and the insulating film 62 may be made of SiO₂ and maybe removed through wet etching. As an example, the wet etching may beperformed using a buffer oxide etchant (BOE).

According to an exemplary embodiment of the present invention, betweenoperations C and D described above, as operation E, an operation offorming a protective film 80 on the side surfaces of the plurality ofmicro-nanofin LED pillars as shown in FIG. 21K may be further performed.The protective film 80 may be formed through, for example, deposition,and may have a thickness of 10 nm to 100 nm, for example, 90 nm, and amaterial thereof may be, for example, alumina. When alumina is used, anALD method may be used as an example of the deposition. In addition, inorder for the deposited protective film 80 to be formed only on the sidesurfaces of the plurality of micro-nanofin LED pillars, the protectivefilm 80 positioned on the portions other than the side surfaces may beremoved through an etching method, for example, a dry etching methodusing ICP. Meanwhile, although the protective film 80 is illustrated inFIG. 21I as surrounding the entire side surface, the protective film 80may not be formed on the entirety or a portion of the portions of theside surface other than the photoactive layer.

Next, as operation D, an operation of separating the plurality ofmicro-nanofin LED pillars from the substrate as shown in FIG. 21M isperformed. The separating may be performed through cutting using acutting mechanism or detachment using an adhesive film, and the presentinvention is not particularly limited in that respect.

In addition, in the above-described manufacturing method of the secondtype (micro-nanofin) ultra-thin LED element, in the separating inoperation D, as in manufacturing of the first (dot or disc) typeultra-thin LED electrode element, the plurality of micro-nanofin LEDpillars 52 may also be obtained from the substrate by performing anoperation of immersing the LED wafer in an electrolyte to thenelectrically connect the LED wafer to any one terminal of a power supplyand electrically connect the other terminal of the power supply to anelectrode immersed in the electrolyte, and then applying power to form aplurality of pores in a first portion, and an operation of applyingultrasonic waves to the LED wafer to separate a plurality of LEDstructures from the first portion in which the plurality of pores areformed.

Pores may be formed in a portion of the first conductive semiconductorlayer (or an n-type conductive semiconductor layer) of each of theplurality of micro-nanofin LED pillars.

Meanwhile, as shown in FIG. 16 , in the micro-nanofin LED element 107,one surface of the element positioned at a side of the polarizationinducing layer among surfaces in a thickness direction thereof in whicheach layer is stacked may be in contact with two adjacent electrodes211/212 or 213/214 of a lower electrode line 200, and the firstconductive semiconductor layer 10, which is opposite to the one surfaceof the element, may be in contact with an upper electrode line 300. Inthis case, due to a protrusion formed on one surface of the firstconductive semiconductor layer 10, the polarization inducing layer 90may be disposed in contact with the lower electrode line 200 with ahigher probability.

In addition, in the lower electrode line 200, a unit electrode area,that is, an area of a region that can be driven independently when themicro-nanofin LED element is arranged on the lower electrode line 200,and then the upper electrode line 300 is disposed on the micro-nanofinLED element, may be preferably in a range of 1 μm² to 100 cm² and morepreferably in a range of 4 μm² to 100 mm², but the unit electrode areais not limited to the above area.

According to an exemplary embodiment of the present invention, as shownin FIG. 16 , in order to reduce contact resistance between themicro-nanofin LED elements 107 disposed on the lower electrode line 200,a conducting metal layer 500 may be further included to connect thelower electrode line 200 and the polarization inducing layer 90 of themicro-nanofin LED element 107 in contact with the lower electrode line200. The conducting metal layer 500 may be a conductive metal layer ofsilver, aluminum, or gold and may be formed to have a thickness of, forexample, about 10 nm.

In addition, an insulating layer 600 may be further included in a spacebetween the lower electrode line 200 and the upper electrode line 300 inelectrical contact with the first conductive semiconductor layer 10corresponding to an upper surface of the self-aligned micro-nanofin LEDelement 107. The insulating layer 600 prevents electrical contactbetween the two electrode lines 200 and 300 which vertically face eachother and performs a function of more easily implementing the upperelectrode line 300.

For the insulating layer 600, a material performing a typical insulatingfunction may be used without limitation. Preferably, the insulatinglayer 600 may be made of a transparent material. As an example, theinsulating layer 600 may be a layer made of an insulating material suchas SiO₂, SiN_(x), Al₂O, HfO₂, or ZrO₂.

The above-described micro-nanofin LED electrode assembly 100 l accordingto an exemplary embodiment of the present invention may be manufacturedby performing a process which includes operation 1 of injecting an inkcomposition including a plurality of micro-nanofin LED elements 107 ontoa lower electrode line 200 including a plurality of lower electrodes211, 212, 213, and 214 spaced a certain interval from each other in ahorizontal direction, operation 2 of applying an assembly voltage to thelower electrode line 200 and self-aligning the micro-nanofin LEDelements 107 such that a first conductive semiconductor layer 10 or apolarization inducing layer 90 of the micro-nanofin LED element 107 in asolution comes into contact with at least 17 adjacent lower electrodes211/212 and 213/214, and operation 3 of forming an upper electrode line300 on the plurality of self-aligned micro-nanofin LED elements 107.

The micro-nanofin LED element of operation 1 may be a rod-type elementwhich has a planar surface having a length and width of a nano or microsize and a thickness perpendicular to the planar surface is shorter thanthe length, and the first conductive semiconductor layer 10, aphotoactive layer 20, a second conductive semiconductor layer 30, andthe polarization inducing layer 90 may be sequentially stacked in athickness direction thereof.

The solution including the plurality of micro-nanofin LED elements 107of operation 1 may include the plurality of micro-nanofin LED elements107 and a solvent performing a function of dispersing and moving theelements on the electrodes of the lower electrode line. In this case,the solution may be in the form of ink or paste and may be injected ontothe lower electrode line 200 using an inkjet. Meanwhile, in operation 1,it has been described that the elements are injected as a solution phasemixed with a solvent, but when the elements are first injected onto thelower electrode line, and then the solvent is added, it is consequentlythe same as a case in which the solution is injected.

The solvent may be at least one selected from the group consisting ofacetone, water, alcohol and toluene and may be more preferably acetone.However, types of the solvent are not limited to those described above,and any solvent that can evaporate well without physically or chemicallyaffecting the micro-nanofin LED element may be used without limitation.Preferably, the micro-nanofin LED elements may be added in an amount of0.001 to 100 parts by weight based on 100 parts by weight of thesolvent. When the micro-nanofin LED elements are added in an amount thatis less than 0.001 parts by weight, the number of micro-nanofin LEDelements connected to the lower electrode may be small, and thus it maybe difficult for the micro-nanofin LED electrode assembly to functionnormally. In addition, there may be a problem in that the solutionshould be added dropwise several times in order to overcome such aproblem. When the micro-nanofin LED elements are added in an amount thatexceeds 100 parts by weight, there may be a problem in that thealignment of each of the micro-nanofin LED elements may be disturbed.

Next, as operation 2, an operation of applying an assembly voltage tothe lower electrode line 200 and self-aligning the micro-nanofin LEDelements 107 such that the first conductive semiconductor layer 10 orthe polarization inducing layer 90 of the micro-nanofin LED element 107in the solution comes into contact with at least 17 adjacent lowerelectrodes 211/212 and 213/214 is performed.

Operation 2 is an operation in which charges are induced in themicro-nanofin LED elements by induction of an electric field formed by apotential difference between the adjacent lower electrodes 211/212 or213/214, and the micro-nanofin LED elements are induced to havedifferent charges from a center of the element to both ends thereof in alength direction of the micro-nanofin LED element, thereby self-aligningthe micro-nanofin LED elements. Among the plurality of lower electrodesof the lower electrode line, power may be applied to form a potentialdifference between any one of the two adjacent lower electrodes and theother or between a first group including two or more adjacent lowerelectrodes and a second group which is adjacent to the first group andincludes two or more adjacent lower electrodes. For a magnitude, type,or the like of the applied assembly voltage, Korean Patent ApplicationNos. 10-2013-41080912, 10-2016-0092737, and 10-2016-0073572 by theinventor of the present invention may be incorporated by reference.

Next, as operation 3, an operation of forming the upper electrode line300 on the plurality of self-aligned micro-nanofin LED elements 107 isperformed. After an electrode line is patterned using knownphotolithography, an electrode material may be deposited, or anelectrode material may be deposited and then be dry- and/or wet-etched,thereby implementing the upper electrode line 300. In this case, sincedescription of the electrode material is the same as the abovedescription of the electrode material of the lower electrode line,description thereof will be omitted here.

Meanwhile, between operations 2 and 3, operation 2-2 of forming aconducting metal layer 500 for connecting the lower electrode line 200and the polarization inducing layer 90 of each micro-nanofin LEDelements 107 in contact with the lower electrode line 200 and operation2-3 of forming an insulating layer 600 on the lower electrode line 200to not cover an upper surface of the self-aligned micro-nanofin LEDelement 107.

A line on which a conducting metal layer is to be deposited may bepatterned by applying a photolithography process using a photosensitivematerial to then deposit the conducting metal layer, or a depositedmetal layer may be patterned and then etched, thereby manufacturing theconducting metal layer 500. Such a process may be performed byappropriately adopting a known method, and Korean Patent Application No.10-2016-41181910 by the inventor of the present invention may beincorporated by reference.

After the conducting metal layer 500 is formed, an operation of formingthe insulating layer 600 on the lower electrode line 200 to not coverthe upper surface of the self-aligned micro-nanofin LED element 107 maybe performed. The insulating layer 600 may be formed by depositing aknown insulating material. As an example, an insulating material such asSiO₂ or SiN_(x) may be deposited through a PECVD method, an insulatingmaterial such as AlN or GaN may be deposited through a MOCVD method, oran insulating material such as Al₂O, HfO₂, or ZrO₂ may be depositedthrough an ALD method. Meanwhile, the insulating layer 600 may be formedat a level to not cover the upper surface of the self-alignedmicro-nanofin LED element 107, and to this end, the insulating layer maybe formed through deposition to a thickness to not cover the uppersurface, or after the insulating layer is deposited to cover the uppersurface, dry etching may be performed before the upper surface of theelement is exposed.

The present invention will be described in more detail through thefollowing examples, however, the following examples do not limit thescope of the present invention, and it should be understood that thefollowing examples are intended to facilitate understanding of thepresent invention.

EXAMPLES Preparation Example 1: Manufacturing of First Type Ultra-ThinLED Element

A typical LED wafer (manufactured by EPISTAR Corporation), in which anundoped n-type III-nitride semiconductor layer, an n-type III-nitridesemiconductor layer doped with Si (with a thickness of 4 μm), aphotoactive layer (with a thickness of 0.45 μm), and a p-typeIII-nitride semiconductor layer (with a thickness of 0.05 μm) weresequentially stacked on a substrate, was provided.

On the provided LED wafer, ITO (with a thickness of 0.15 μm) as a lowerelectrode layer, SiO₂ (with a thickness of 1.2 μm) as a first masklayer, and Al (with a thickness of 0.2 μm) as a second mask layer weresequentially deposited, and then a spin-on glass (SOG) resin layer ontowhich a pattern was transferred was transferred onto the second masklayer using a nanoimprint apparatus.

Thereafter, the SOG resin layer was cured using RIE, and a residualresin portion of the resin layer was etched through RIE to form a resinpattern layer. After that, the second mask layer was etched along apattern using ICP, and the first mask layer was etched using RIE. Next,after the lower electrode layer, the p-type III-nitride semiconductorlayer, and the photoactive layer were etched using ICP, the doped n-typeIII-nitride semiconductor layer was etched to a thickness of 0.78 μm tomanufacture an LED wafer on which a plurality of LED structures (with adiameter of 850 nm and a height of 850 nm) were formed through KOH wetetching in order to implement a side surface of the etched doped n-typeIII-nitride semiconductor layer to be perpendicular to a layer surface.

Thereafter, a protective film material of SiN, was deposited on the LEDwafer on which the plurality of LED structures were formed (todeposition thicknesses of 52.5 nm and 72.5 nm based on a side surface ofthe LED structure, see a scanning electron microscope (SEM) images ofFIG. 22A-FIG. 22C and FIG. 23A-FIG. 23C), and then the protective filmmaterial formed between the plurality of LED structures was removedthrough a reactive ion etcher to expose an upper surface S₁ of a firstportion a of the doped n-type III-nitride semiconductor layer.

After that, the LED wafer on which a temporary protective film wasformed was immersed in an electrolyte solution of 0.3 M of oxalic acidand then connected to an anode terminal of a power supply, a cathodeterminal was connected to a platinum electrode immersed in theelectrolyte, and then a voltage of 10 V was applied for 5 minutes toform a plurality of pores from the surface of the first portion a of thedoped n-type III-nitride semiconductor layer to a point at a depth of600 nm as shown in a SEM images of FIG. 24A-FIG. 24B. Next, after thetemporary protective film was removed through RIE, a surface protectivefilm made of Al₂O₃ was deposited again on the LED wafer to a thicknessof 50 nm based on the side surface of the LED structure, and the surfaceprotective film formed on the plurality of LED structures and thesurface protective film formed on the surface S1 of the first portion aof the doped n-type III-nitride semiconductor layer were removed throughICP to expose the upper surface S₁ of the first portion a of the dopedn-type III-nitride semiconductor layer and an upper surface of the LEDstructure.

Then, after the LED wafer was immersed in a bubble-forming solution ofgamma-butyllactone, the pores formed in the doped n-type III-nitridesemiconductor layer were collapsed using bubbles generated by radiatingultrasonic waves at a frequency of 40 kHz for 10 minutes, therebymanufacturing an ultra-thin LED element assembly including ultra-thinLED elements in which the plurality of LED structures were separatedfrom the wafer as shown in an SEM images of FIG. 25A-FIG. 25B. Inaddition, it can be confirmed that there is no non-separated LEDstructure on the wafer as shown in FIG. 25A and FIG. 25B. In this case,FIG. 25A is a side view of a wafer from which ultra-thin LED devices areseparated, and FIG. 25B is a top-down view.

Comparative Preparation Example 1: Rod-Type LED Element

A rod-type LED element assembly having a diameter of 650 nm and a heightof 4.2 μm and the same stacked structure as in Example 1 wasmanufactured from an LED wafer through a typical method.

Experimental Example 1

After each of the LED element assemblies manufactured in PreparationExample 1 and Comparative Preparation Example 1 was introduced intoacetone, ultrasonic waves were radiated under 100 W conditions todisperse LED elements, a dispersion state of the LED elements waschecked by measuring absorbance for 2 hours at 15-minute intervals, anda spectral area of a visible light region of 380 nm to 780 nm wasnormalized using measured results and is shown in an absorbance graphfor each time in FIG. 26 .

As can be confirmed from FIG. 26 , it can be seen that an ultra-thin LEDelement according to Preparation Example 1 has excellent dispersionretention performance in an acetone solvent for a long time as comparedwith a rod-type LED element according to Comparative Preparation Example1.

Example 1: Manufacturing of Ultra-Thin LED Electrode Assembly

An ultra-thin LED element assembly was manufactured in the same manneras in the ultra-thin LED element provided in Preparation Example 1except that, before separation from an LED wafer through ultrasonicwaves, a Ti/Au layer (thickness of 10 nm/100 nm) was further formed asan electrode layer on a lower electrode layer, and then a bonding layerin which a thiol group was exposed was formed by treating1,2-ethanedithiol on the Ti/Au layer.

Thereafter, a lower electrode line including the lower electrode wasimmersed in an ink composition including the ultra-thin LED elementassembly, and ultra-thin LED elements were erected on the lowerelectrode for a certain time and assembled. In this case, the usedultra-thin LED element had a diameter of 750 nm and a height of 1.1 μm.

Then, after SiO₂ as an insulating layer serving as an insulator wasformed to a thickness of 1.4 μm to 1.6 μm, the insulating layer formedto a corresponding thickness was etched to expose n-GaN of theultra-thin LED element by a thickness of 300 nm to 400 nm, and thenaluminum zinc oxide (AZO) or ITO used as a transparent electrode wasdeposited to a thickness of 150 nm on the exposed ultra-thin LED elementto form an upper electrode line including an upper electrode on theultra-thin LED element, thereby manufacturing the ultra-thin LEDelectrode assembly having a width of 0.3 mm and a length of 0.3 mm.

In the ultra-thin LED electrode assembly, one pixel unit included threesubpixel units, and the three subpixel units included a first subpixelunit including an ultra-thin blue LED element, a second subpixel unitincluding an ultra-thin green LED element, and a third subpixel unitincluding an ultra-thin red LED element.

Each of the three subpixel units included six ultra-thin LED elements.

Experimental Example 2

Power was applied to the upper electrode line and the lower electrodeline of the ultra-thin LED electrode assembly provided in Example 1, anultra-thin LED electrode assembly emitting light and having 1,000 PPIwas manufactured, and it was confirmed that dark spots in the pixel didnot occur.

According to an ultra-thin LED element applied to a high-resolutionultra-thin LED display of the present invention, while a light emittingarea of the element is increased, an area of a photoactive layer exposedat a surface can be considerably reduced to prevent or minimize adecrease in efficiency due to surface defects, thereby implementing anelectrode assembly having excellent quality. Furthermore, in a used LEDelement, a decrease in electron-hole recombination efficiency due tonon-uniformity between electron and hole velocities is minimized tominimize a decrease in luminous efficiency, thereby more easilyimplementing an electrode assembly.

According to an ultra-thin LED display of the present inventionmanufactured using such an ultra-thin LED element, compared with anexisting LED display such as an existing micro-LED, a thickness isreduced, a response speed is improved, a color area is improved, aviewing angle is increased, and brightness is increased, and it is alsopossible to reduce a display defect rate due to vacancies of LEDelements, misalignment, and the like that occur when a subpixel ismanufactured.

Although exemplary embodiments of the present invention have beendisclosed, it will be apparent that various changes, modifications, andequivalents may be made thereto and the exemplary embodiments may beadequately modified and applied in the same manner. Therefore, theforegoing description in no way limits the scope of the presentinvention, which shall be defined by the claims appended hereto.

What is claimed is:
 1. A high-resolution ultra-thin light-emitting diode(LED) display for augmented reality (AR) and virtual reality (VR)devices, comprising an ultra-thin LED electrode assembly which includes:a plurality of lower electrodes formed on a substrate; a plurality ofpixel units formed on the lower electrodes; an insulating layer formedon the substrate and the plurality of pixel units; and a plurality ofupper electrodes formed on the insulating layer, wherein each of theplurality of pixel units includes subpixel units each including aplurality of ultra-thin LED elements.
 2. The high-resolution ultra-thinLED display of claim 1, wherein: the subpixel unit includes three ormore ultra-thin LED elements; and the ultra-thin LED element includes atleast one selected from among an ultra-thin blue LED element, anultra-thin green LED element, and an ultra-thin red LED element.
 3. Thehigh-resolution ultra-thin LED display of claim 1, wherein: each of theplurality of pixel units includes three or four subpixel units; and eachof the three or four subpixel units includes 3 to 30 ultra-thin LEDelements.
 4. The high-resolution ultra-thin LED display of claim 3,wherein each of the three or four subpixel units has a circular shape, arectangular shape, or a square shape.
 5. The high-resolution ultra-thinLED display of claim 3, wherein: each of the plurality of pixel unitsincludes three subpixel units; and the three subpixel units include afirst subpixel unit including an ultra-thin blue LED element, a secondsubpixel unit including an ultra-thin green LED element, and a thirdsubpixel unit including an ultra-thin red LED element.
 6. Thehigh-resolution ultra-thin LED display of claim 3, wherein all of thethree or four subpixel units include an ultra-thin blue LED element. 7.The high-resolution ultra-thin LED display of claim 6, wherein at leastone color conversion layer selected from a green color conversion layerand a red color conversion layer is further stacked on the upperelectrode.
 8. The high-resolution ultra-thin LED display of claim 1,wherein: each of the plurality of ultra-thin LED elements constitutingthe subpixel unit includes a first conductive semiconductor layer, aphotoactive layer, and a second conductive semiconductor layer which arestacked; and the ultra-thin LED elements are erected and disposed in thesubpixel unit such that the first conductive semiconductor layer of theultra-thin LED element faces the lower electrode.
 9. The high-resolutionultra-thin LED display of claim 1, wherein the ultra-thin LED elementincludes at least one selected from: a dot or disc LED element which hasa thickness of 2,000 nm or less in a stacking direction of layers,wherein the dot LED element has a ratio between the thickness and alength of a major axis in a cross section perpendicular to the stackingdirection in a range of 1:0.5 to 1:1.5, and the disc LED element has aratio between the thickness and a length of a major axis in a crosssection perpendicular to the stacking direction in a range of 1:1.5 to1:5.0; and a micro-nanofin LED element which has a thickness of 100 nmto 2,000 nm in a stacking direction of layers and in which a length of amajor axis in a cross section perpendicular to the stacking direction isin a range of 100 nm to 6,000 nm, and a ratio between the thickness andthe length of the major axis is 1:3 or more.
 10. The high-resolutionultra-thin LED display of claim 9, wherein: the ultra-thin LED elementfurther includes an arrangement guide layer, which is for erecting andarranging the ultra-thin LED element in a thickness direction thereof,at one side of the ultra-thin LED element in the thickness direction andone side or both sides of a region in the lower electrode in which theultra-thin LED element is to be disposed; and the arrangement guidelayer is a magnetic layer, a charge layer, or a bonding layer.
 11. Thehigh-resolution ultra-thin LED display of claim 8, wherein: the firstconductive semiconductor layer of the ultra-thin LED element is ann-type III-nitride semiconductor layer; and the ultra-thin LED elementfurther includes an electron delay layer on an opposite surface oppositeto one surface of the first conductive semiconductor layer adjacent tothe photoactive layer such that the numbers of electrons and holesrecombined in the photoactive layer are balanced.
 12. Thehigh-resolution ultra-thin LED display of claim 11, wherein: the firstconductive semiconductor layer is a doped n-type III-nitridesemiconductor layer; and the electron delay layer is a III-nitridesemiconductor having a lower doping concentration than the firstconductive semiconductor layer.
 13. The high-resolution ultra-thin LEDdisplay of claim 8, wherein: the second conductive semiconductor layerof the ultra-thin LED element is a p-type III-nitride semiconductorlayer; and the ultra-thin LED element further includes an electron delaylayer on an opposite surface opposite to one surface of the secondconductive semiconductor layer adjacent to the photoactive layer suchthat the numbers of electrons and holes recombined in the photoactivelayer are balanced.
 14. The high-resolution ultra-thin LED display ofclaim 8, wherein: the first conductive semiconductor layer of theultra-thin LED element is an n-type III-nitride semiconductor layer; thesecond conductive semiconductor layer is a p-type III-nitridesemiconductor layer; and the ultra-thin LED element further includes atleast one film of: a hole pushing film which surrounds an exposed sidesurface of the second conductive semiconductor layer or the exposed sidesurface of the second conductive semiconductor layer and an exposed sidesurface of at least a portion of the photoactive layer to move holes ata side of the exposed side surface toward a center; and an electronpushing film which surrounds an exposed side surface of the firstconductive semiconductor layer to move electrons at a side of theexposed side surface side toward a center.
 15. The high-resolutionultra-thin LED display of claim 14, wherein: the ultra-thin LED elementincludes both the hole pushing film and the electron pushing film; andthe electron pushing film is provided as an outermost film surroundingthe side surfaces of the first conductive semiconductor layer, thephotoactive layer, and the second conductive semiconductor layer. 16.The high-resolution ultra-thin LED display of claim 9, wherein, when theultra-thin LED element is a micro-nanofin LED element, the micro-nanofinLED element includes a polarization inducing layer that is furtherstacked on the second conductive semiconductor layer.
 17. Thehigh-resolution ultra-thin LED display of claim 16, wherein, when theultra-thin LED element is the micro-nanofin LED element, the firstconductive semiconductor layer or the polarization inducing layer of themicro-nanofin LED element is disposed in contact with at least twoadjacent lower electrodes.
 18. The high-resolution ultra-thin LEDdisplay of claim 1, wherein the high-resolution ultra-thin LED displayhas a resolving power of 450 pixels per inch (PPI) to 3,000 PPI.
 19. Amanufacturing method of a high-resolution ultra-thin light-emittingdiode (LED) display, which includes an ultra-thin LED electrodeassembly, for augmented reality (AR) and virtual reality (VR) devices,wherein the ultra-thin LED electrode assembly is formed by performing aprocess which includes: operation 1 of providing a lower electrode lineincluding a lower electrode; operation 2 of forming a plurality of pixelunits on the lower electrode; operation 3 of filling a periphery ofultra-thin LED elements in each of the plurality of pixel units with aninsulator to form an insulating layer; and operation 4 of forming anupper electrode line, which includes an upper electrode, to beelectrically connected to an opposite side of the ultra-thin LED elementopposite to one side of an ultra-thin LED element assembled on the lowerelectrode, wherein: each of the plurality of pixel units in operation 2is formed of subpixel units each including the plurality of ultra-thinLED elements; and the subpixel units are formed by printing theplurality of ultra-thin LED elements on the lower electrode through aninkjet printing method, a laser-assisted transfer printing method, astamp transfer printing method, a magnetic field induction printingmethod, or an electric field induction printing method.